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Full text of "New essentials of biology presented in problems"


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BOOK 570.H92 EDUCATION cj 
HUNTER # NEW ESSENTIALS OF 
BIOLOGY 



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NEW 
ESSENTIALS OF BIOLOGY 

PRESENTED IN PROBLEMS 



BY 
GEORGE WILLIAM HUNTER. PH.D. 

PROFESSOR OF BIOLOGY, KNOX COLLEGE, GALESBURG, ILLINOIS 

FORMERLY HEAD OF DEPARTMENT OF BIOLOGY 

DeWITT CLINTON HIGH SCHOOL, NEW YORK 




AMERICAN BOOK COMPANY 

NEW YORK CINCINNATI CHICAGO BOSTON ATLANTA 



COPYKIQHT, 1911, BY 

GEORGE WILLIAM HUNTER. 

Copyright, 1923, 1928, by 

AMERICAN BOOK COMPANY. 

All Rights Reserved. 



HUNTER, NEW ESSENTIALS OF BIOLOQT. 
W.P. 22 



li L37 



MADE TN U. S. A. 



THE PLA.N AND PURPOSE OF THIS BOOK 

The plan of this book recognizes first-year biology as a science 
founded upon certain imderlytng and basic principles. These 
principles underhe not only biology, but also organized society. 
The culmination of such an elementary course is avowedly the 
understanding of man, and the principles which hold together 
such a course should be chiefly physiological. The functions of 
all living things, plants or animals, movement, irritabihty, nu- 
trition, respiration, excretion, and reproduction; the interrelation 
of plants and animals and their economic relations, all these as 
they relate to man should enter into a course in elementary biology. 

But to make plain these physiological processes, difficult even 
for an advanced student of biology to comprehend, the simplest 
method of demonstration is necessary. Plant physiology, be- 
cause of the ease with which simple demonstrations can be made, 
is more profitable ground for beginners than is the physiology 
of animals. The foods which animals use are manufactured and 
used by green plants; the action of the digestive enzymes, the 
principle of osmosis, and the subject of reproduction can better 
be first handled from the botanical aspect. The topics just 
mentioned introduced from the standpoint of the botanist gain 
much by repetition from the zoological angle. The principles of 
physiology, after being appHed in experiment to plants and 
animals, emerge in final clarity when appHed at the last to 
man, — the most complex of all hving things. 

One sufficient reason for the placing of a course in biology in 
the first year of the secondary course lies in the fact that at 
this time the child is receptive to the message of apphed biology. 
Private and public hygiene, the message of protective medicine 
and sanitation, the story of pure milk and of pure water and 
what they mean to a community; all these things can most 
logically be presented in a course that makes man the center. 
The allied topics of conservation of plant and animal life, the 

V 



vi PLAN AND PURPOSE OF THIS BOOK 

destruction of haniifiil plants and animals, the relation of insects 
and other animals to the spread of disease, and the work of civic 
and government departments in the development of nature's 
gifts and in the preservation of national health should be treated 
in their relation to man. 

Moreover, the data given should be treated from the biological 
standpoint, not that of botany, zoolog}^, or human physiology. 
Ideally, we might take up general principles and draw from the 
great storehouses of plant, animal, and human biology" to il- 
lustrate each principle before going on to the next. Practically, 
however, such a plan does not seem to be workable, partly be- 
cause of the difficult}^ of collecting enough material to make such 
demonstrations possible. It is impracticable with immature stu- 
dents, because they cannot grasp the many-sidedness of the 
apphcation at once. This will come only after repetition of the 
principle, each time from a shghth' different point of ^dew. 

It frequenth' happens that the related study of plants and ani- 
mals may be taken up to advantage. Insects and flowers, both 
plentiful in the faU, ma}' weU be studied together for the relation 
of life habits and adaptations in the insect to cross-pollination 
of flowere. Apphed biolog}', in its relation to plants or to ani- 
mals, must of com'se be 'treated from all sides. The fungi and 
the bacteria in their relations to man are conspicuous examples. 

Teachers often spend too much time in teaching unessentials 
taken from an immense field, and do not spend enough time in 
emphasizing from constanth" varied points of attack the fimda- 
merital truths on which the science of biology is built. The pages 
which follow are an attempt to drive home by repetition, and 
from many points of view, some of the important principles of 
physiological biologj^ 

The plan of the book includes the sohdng of a number of 
problems in biolog}', each of which is more or less deteimined 
by the one immediately preceding it. So far as possible, the 
problems have a human interest. Abstractions are not part of 
the thought of a first-year pupil. Concrete problems, related 
when possible to the daily life of the pupil, have been used. 
The problems are stated in the form of laboratory exercises or 
suggestions, the material for which is in the hands of the pupil 



PLAN AND PURPOSE OF THIS BOOK vii 

or is worked out as a demonstration before the class. In all 
cases the laboratory types or physiological experiments demon- 
strate some important principle of biology. 

The laboratory exercise immediately precedes the textbook 
discussion, the latter being used to clear up any false inferences 
the pupil may have made from the specimen in hand and to fix 
the object of the problem in the mind of the pupil. Too often 
has a laboratory exercise meant nothing to a pupil but ''busy 
work." A plainly outlined and organized plan of attack, a few 
references to the text or tc previous work performed, and a 
definite problem wiU result in better and more definite laboratory 
work. For use with this book manuals for the solution of 
laboratory problems have been prepared by my coworker, Mr. 
R. W. Sharpe, and by myseK. The latter manual, ''Laboratory 
Problems in Civic Biology," gives an excellent point of attack 
through the interests of the student and gives a varied selection 
of problems for the teacher. 

Two styles of type have been used in the text. The larger 
type contains material which is believed to be of first impor- 
tance, the smaller type the less important topics. There are 
always some students whose grasp of subject matter or whose 
maturity places them above the average student. It is expected 
that the material in smaU type wiU be used to advantage with 
such students. Thus the material in small print will, to an 
extent, take the place of outside assigned reading and will, as 
well, give problem and project suggestions to those students 
whose interests are keenly biological. 

The manuscript in its entirety was read by Professor H. E. 
Walter of Brown University, and by Miss A. P. Hazen, Head of 
the Department of Biology in the Eastern District High School; 
to them I owe sincere thanks for many helpful criticisms and 
suggestions. Acknowledgments are also due to H. G. Barber, 
E. A. Bedford, John E. McCarthy, and R. W. Sharpe of the 
DeWitt CKnton High School, and to Mr. C. W. Beebe, Curator 
of Birds, New York Zoological Park, for their careful reading 
and criticism of parts or all of the proof. 

Thanks are due, also, to Professor E. B. Wilson, Mr. William 
C. Barbour, Dr, John A. Sampson, W. C. Stevens and C. W. 



viii PLAN AND PURPOSE OF THIS BOOK 

Beebe, Alvin Davison, and Dr. Frank Overton; to the United 
States Department of Agriculture; the New York Aquarium; 
the Charity Organization Society; the Folmer and Schwing 
Company, Rochester, N. Y.; and the American Museum of 
Natural History, for permission to copy and use certain photo- 
graphs and cuts which have been found useful in teaching. 
R. W. Coryell and J. W. Tietz, two of my former pupils, made 
several of the photographs of experiments. Many of the line 
drawings in this revision are the work of Frank M. Wheat, 
whose scientific and artistic conceptions have added much to 
the value of the book. 

At the end of each chapter is a list of books which have 
proved their use either as reference reading for students or as 
aids to the teacher. Most of the books mentioned are within 
the means of the small school. Two sets are expensive: one, 
The Natural History of Plants, by Kerner, translated by Oliver, 
published by Henry Holt and Company, in two volumes; the 
other, Plant Geography upon a Physiological Basis, by Schimper, 
published by the Clarendon Press; but both works are invaluable 
for reference. 

For a general introduction to physiological biology, the follow- 
ing are most useful and inspiring books: Parker, Lessons in 
Elementary Biology, The Macmillan Company; Sedgwick and Wil- 
son, General ^Biology, Henry Holt and Company; Shull, Principles 
of Animal Biology, McGraw-Hill Company. 

Three books stand out from the pedagogical standpoint as by 
far the most helpful of their kind on the market. No teacher of 
botany or zoology can afford to be without them. They are: 
Lloyd and Bigelow, The Teaching of Biology, Longmans, Green, 
and Company; C. F. Hodge, Nature Study and Life, Ginn and 
Company; and Twiss, Principles of Science Teaching, The Mac- 
millan Company. The last-named book gives the modern peda- 
gogical interpretation of the introductory sciences. Other books 
of value from the teacher's standpoint are: Ganong, The Teach- 
ing Botanist, The Macmillan Company; L. H. Bailey, The Nat- 
ure Study Idea, Doubleday, Page and Company; and McMurry's 
How to Study, Houghton Mifflin Company. 



CONTENTS 

CHAPTER PAGE 

I. Some Reasons for the Study of Biology 1 

II. The Environment of Living Things 5 

III. The Functions and Composition of Living Things . . 16 

IV. Flowers and their Work 23 

V. Fruits and their Uses 40 

VI. Seeds and Seedlings 54 

VII. Roots and their Work . 70 

VIII. The Structure and Work of the Stem 84 

IX. Leaves and their Work .' 98 

X. Our Forests; their Uses and the Necessity for their 

Protection 116 

XI. The Various Forms of Plants and how they Reproduce 

Themselves 126 

XII. How Plants are modified by their Surroundings . . 136 

XIII. How Plants benefit and harm Mankind 146 

XIV. The Relations of Plants to Animals 166 

XV. The Protozoa 172 

XVI. Simple Metazoa — Division of Labor 181 

XVII. The Worms, a Study of Relations to Environment . 194 

XVIII. The Crayfish. A Study of Adaptations 204 

XIX. The Insects ' . 216 

XX. General Considerations from the Study op Insects . 234 

XXI. The Mollusks 253 

XXII. The Vertebrate Animals 261 

Fishes 262 

Amphibia. The Frog 272 

is 



X CONTENTS 

CHAPTER PAGE 

Reptiles 281 

BiRR« 286 

Mammals 303 

XXIII. Man, A Mammal 3x1 

XXIV. Foods and Dietaries 322 

XXV. Digestion and Absorption 343 

XXVI. The Blood and its Circulation 358 

XXVII. Respiration and Excretion 374 

XXVIII. The Nervous System and Organs of Sense 390 

XXIX. Good Health and How to Keep It 404 

XXX. Health and Disease. A Chapter on Civic Biology . 415 

Glossary 427 

Index 441 



NEW ESSENTIALS OF BIOLOGY 



I. SOME REASONS FOR THE STUDY OF BIOLOGY 

What is Biology? — Biology is the study of living beings, both 
plant and animal. Inasmuch as man is an animal, the study of 
biology includes the study of man in his relation to the plants 
and the animals which surround him. Most important of all 
is that branch of biology which treats of the mechanism we call 
the human body, — of its parts and their uses, and its repair. 
This subject we call human physiology. 

Why study Biology? — Although biology is a very modern 
science, it has found its way into most high schools; and an 
increasingly large number of boys and girls are engaged in 
its study. The question might well be asked by any of these 
students, Why do I take up the study of biology? Of what 
practical value is it to me? Aside from the discipline it gives 
me, is there anything that I can get from it which will help me 
in my future life as a boy or girl with only a high school 
education? 

Human Physiology. — The answer to this question is plain. 
If the study of biology will give us a better understanding of 
our own bodies and their care, then it certainly is of use to us. 
That phase of biology known as physiology deals with the uses 
of the parts of a plant or animal; human physiology deals with 
the uses, and hygiene (hi'ji-en) with the care, of the parts of the 
human animal. Much sickness may be prevented by living ac- 
cording to the laws which hygiene teaches. It is estimated 
that 400,000 out of the 1,600,000 deaths that occur yearly 
in this country could be averted if only every one lived in a 
hygienic (hi-ji-en'ik) manner. In its application to the life of 
each of us, as a member of a family, as a member of the school 
we attend, and as a future citizen, a knowledge of hygiene is 
of the greatest importance. 

1 



REASONS FOR THE STUDY OF BIOLOGY 



Relations of Plants to Animals. — But there are other reasons 
why an educated person should know something about biology. 
We do not always reahze that if it were not for the green 
plants, there would be no animals on the earth. Green plants 
furnish animals with their food. Even the meat-eating animals 
feed in the long run upon those that feed upon plants. How 

the plants manufacture 
this food and the relation 
they have to animals will 
be discussed in later 
chapters. Plants furnish 
man with the greater part 
of his food in the form of 
grains and cereals, fruits 
and nuts, edible roots 
and leaves; they provide 
his domesticated animals 
with food; they give him 
timber for his bouses and 
wood and coal for his 
fires; they provide him 
with pulp wood, from 
which he makes his paper, 
and oak galls, from which 
he obtains ink. Much of 
man's clothing and the 
thread with which it is 
sewed come from fiber- 
producing plants. Most 
medicines, beverages. 

Banana plants. Each plant bears one bunch flavoring extracts, and 

^"^ P^^°*' spices are plant products, 
while plants are made use 
of in hundreds of ways in the useful arts and trades, producing 
varnishes, dyestuffs, rubber, and other products. 

Bacteria in their Relation to Man. — In still another way, cer- 
tain tiny plants vitally affect mankind. These plants, so small 
that miUions can exist in a single drop of fluid, are called bacte^ria 




of bananas and is then cut down, 
grow up from the root. 



BACTERIA, ANIMALS 3 

or germs. Existing almost everywhere about us, — in water, 
soil, food, and the air, — they play a tremendous part in shap- 
ing the destiny of man on the earth. They help him in that 
they act as scavengers, causing things to decay; they give flavor 
to cheese and butter; they assist the tanner, and are invaluable 
to the farmer; but they hkewise cause decay of our meat and 
fish, and our vegetables and fruits; they sour our milk, and 
spoil om* canned goods. More than this, they cause diseases, 
among others tuberculo'sis, a disease so harmful as to be called 
the " white plague." Fully one half of the deaths each year are 
caused by these plants. So important are bacteria that a 
subdivision of biology, called hacterioV ogy , has been named after 
them, and hundreds of scientists are devoting their Uves to the 
study of germs and their control. The greatest of all bacteri- 
ologists, Louis Pasteur (pas-tur')/ once said, " It is within the 
power of man to cause all parasitic diseases [diseases caused 
mostly by bacteria] to disappear from the world." His prophecy 
is gradually being fulfilled, and it may be the lot of some boys 
or girls who read this book to do their share in helping to bring 
about this condition of affairs. 

Harmful Relation of Animals to Man. — Animals play an im- 
portant part in the world in causing and carrying disease. Ani- 
mals that cause disease are usually tiny, and live upon other 
animals as parasites; that is, they get their living from their 
hosts on which they feed. Among the diseases caused by para- 
sitic animals are malaria, yellow fever, sleeping sickness, and 
hookworm disease. Animals also carry disease, especially the 
flies and mosquitoes ; rats and other animals are well known 
also as spreaders of disease. From a money standpoint, insects 
do much harm. It is estimated that in this country alone in 1922 
they were responsible for over $2,000,000,000 worth of damage to 
crops, stored foods, and forest products. 

The Uses of Animals to Man. — We aU know the uses man 
has made of .domesticated animals for food and as beasts of 
burden. But many other uses are found for animal products, 
and materials made from animals. Wool, furs, leather, hides, 
and feathers are examples. The arts make use of ivory, tortoise 

1 The diacritic marks are those used in the Webster school dictionaries. 



REASONS FOR THE STUDY OF BIOLOGY 



shell, coral, and mother of pearl; from animals also come 
certain perfumes and oils, glue, lard, and butter; animals produce 
honey, wax, milk, eggs, silk, and various other commodities. 




The silkworm: 1, eggs; 2, larva or silkworm; 3, cocoon spun by the larva; 4, the 
adult moth, which comes from the cocoon and lays the eggs from which new 
larvae are hatched. The cocoons are made of silk threads, which can be unwound. 

The Conservation of our Natural Resources. — Still another 
reason why we should study biology is that we may work in- 
telligently for the conser- 
vation of our natural 
resources, especially our 
forests. The forest, aside 
from its beauty and its 
health-giving properties, 
holds water in the earth. 
It keeps the water from 
drying out of the earth on 
hot days and from running 
off on rainy days. Thus 
a more even supply of 
water is given to our rivers, 
and freshets are prevented. 
Countries that have been 
deforested, such as parts of 
China, Italy, and France, 
are now subject to floods, 
and are in many places 




Raising silkworms in Japan. The silkworms 
are fed on mulberry leaves and must be care- 
fully tended. 



barren. On the forests depend our supply of timber and to a 
large extent OTir future water power. 

Plants and Animals mutually Helpful. — The study of biology 
also shows us the interrelation existing between plants and ani- 



RELATIONS OF PLANTS AND ANIMALS 5 

mals on the earth. Most plants and animals stand in an atti- 
tude of mutual helpfulness: plants providing food and shelter 
for animals; animals giving off waste materials useful to plants 
in the making of food. We learn also that plants and animals 
need the same conditions in their surroundings in order to live; 
water, air, food, a favorable temperature, and usually light. 
We learn that the life processes of both plants and animals 
are essentially the same, and that the living matter of a tree 
is as much alive as is the living matter in a fish, a dog, or a 
man. 

Biology in its Relation to Society. — Finally, the study of 
biology should be part of the education of every boy and girl, 
because society itself is founded upon the principles which biol- 
ogy teaches. Plants and animals are living things, each taking 
what it can from its surroundings; they enter into competi- 
tion with one another, and those which are the best fitted for life 
outstrip the others. Health and strength of body and mind are 
factors in man which tell in winning. The strong may hand 
down to their offspring the characteristics which make them the 
winners. 

Man has made use of this message of nature, and has devel- 
oped improved breeds of horses, cattle, and other domestic ani- 
mals. Plant breeders have hkewise selected plants and seeds 
with great care and thus have stocked the earth with hardier 
and more fruitful domesticated plants. Man^s dominion over 
the living things of the earth is tremendous. It is due to the 
understanding of the principles which underlie the science of 
biology. 

Problem Questions. — 1. WHiy should biology be studied by 
all girls and boys of high school age? 

2. Of what use to the average citizen is a knowledge of 
biology? 



HUNT. NEW E8. — 2 



II. THE ENVIRONMENT OF LIVING THINGS 

Environment. — Living plants and animals are surrounded by 
various substances and forces. Air, light, water, the presence 
or absence of food, changing conditions of temperature, even such 
a force as electricity, may influence the growth or behavior of any 
living thing. Plants and animals take some outside substances 
into their bodies and are externally influenced by others. The total 
of all the surrounding forces which act upon living things helps 
to form their envi'ronment. We shall later see that the environ- 
ment may cause great changes to take place in the structure or 
habits of a plant or animal. It is the purpose of this chapter 
to try to explain something of how plants and animals are influ- 
enced by the factors of their environment. 

In order to understand better what a living plant or animal 
takes from its environment, we must find out something about 
the air, water, and the soil, for it is with these factors that the 
plant and the animal are in immediate contact. 

Problem. How to learn the 'part played hy the common elements 
in the environment of living things, (Laboratory Manual,^ Prob. I; 
Laboratory Problems,^ Probs. 37, 38, 39, 40.) 

(a) Nitrogen. 

(6) Oxygen and oxidation. 

(c) Hydrogen. 

(d) Carbon and carbon dioxide. 

The Composition of the Air. — If we invert a large bell jar over 
a deep tray containing water, having previously placed a float 
holding a bit of burning phosphorus (fos'for-us) upon the surface 
of the water, we find that, as the phosphorus burns, the water 

1 Sharpe, A Laboratory Manual for the Solution of Problems in Biology, Ameri- 
can Book Company. 

'Hunter, Laboratory Problems m Civic Biology, American Book Company. 

6 



CHEMICAL ELEMENTS 




Experiment to show the amount of 
oxygen in the air. A before, and B 
after the phosphorus p is lighted. 



slowly rises in the jar. After a little the fire goes out. The 
water now displaces a volume equal to about one fifth of the 
space occupied by the air in the jar. When the water reaches 
this height, it goes no higher, and, no matter how many times 
or how . parefully the experiment is repeated, the phosphorus 

always stops burning when 
the water displaces one fifth 
of the air in the jar. 

Evidently, the burning of 
the phosphorus uses up some 
gas within the jar which 
supports the flame, and the 
gas which remains in the 
jar, occupying about four 
fifths of the space, does not 
have the power to maintain 
the flame. The former gas is 
oxygen (ox'i-jen); nearly all 
the latter is ni'trogen. These two gases form the principal 
constituents of the air in nearly the proportion seen in the ex- 
periment. The white gas formed by the combination of the 
oxygen with the phosphorus is absorbed by the water in the 
tray. 

Chemical Elements. — All the materials of this universe, both 
living and lifeless, are classified by chemists as either chemical 
elements or chemical compounds. A chemical element is a substance 
which chemists have not been able to break up or decompose into 
simpler substances. Examples of elements are oxygen, making up 
about 20 per cent of the atmosphere; nitrogen, composing nearly 
all the remainder of pure air; carbon, an element that enters into 
the composition of all organic matter; and over seventy others 
of more or less importance to us in the study of biology. 

Nitrogen. — The physical properties (those which we determine 
through our senses) of nitrogen are its lack of color, taste, and odor. 
Its chief chemical characteristics are its inability to support com- 
bustion and its slight tendency to combine with other substances. 
We shall later find that nitrogen is one of the most important 
chemical elements found in living matter. In spite of this, animals 



8 



THE ENVIRONMENT OF LIVING THINGS 




and most plants are absolutely unable to take any nitrogen from 

the air, no matter how much they may need it. 
The other principal element in the air, oxj^gen, is taken out bj" 

plants and animals. We shall be able to see how, after studying 

the properties of oxygen. 

Preparation of Oxygen. Elements and Compounds. — Oxygen 

may be prepared by heating half a teaspoonful of chlorate of 

potash with a Uttle less than its bulk of black oxide of man- 
ganese in a test tube 
over a flame. The chlo- 
rate of potash and oxide 
of manganese are made 
up of chemical elements 
which have united to form 
chemical compounds. A 
combination of two or 
more elements according 

The mixture of chemicals in the test tube M ^^ certain laWS is called a 
is decomposed by heat and gives off the gas CX)mpOUnd. In the mix- 

wX!" ^' ""^'"^ ^ '""'^''''"^ ^"^ displacing ^^^ ^f ^^^ compounds 

named above heat will 
free the oxygen, as is proved by a glowing match end bursting 
into flame when held over the mouth of the test tube, or by 
testing the gas collected in a bottle as shown in the Figure. 
We have decomposed the two chemical compounds and in the 
process we have released the element oxygen. This is an 
example of a chemical change. 

Properties of Oxygen. — Oxygen, when carefuU}^ prepared, is 
found to be colorless, odorless, and tasteless. Combined with 
other substances, it forms a very large part by weight of water 
rocks, minerals, and the bodies of plants and animals. 

Oxygen has the very important propert}^ of uniting with 
many other substances. The chemical union of oxygen with 
another substance is called oxidation. Rapid oxidation produces 
a flame or light. Oxidation, either rapid or slow, may take 
place wherever oxygen is present. This fact has a far-reaching 
significance in the imderstanding of the most important problems 
of biology. 



OXIDATION 9 

Oxidation in a Match. — The simple process of striking a sulphur match 
gives us an illustration of this process of oxidation. The head of the 
match is formed of a combination of phosphorus, sulphur, and some other 
materials. Phosphorus is a chemical element distinguished by its extreme 
infiammabiUty; that is, it unites with oxygen at a comparatively low tem- 
perature, producing a flame. Sulphur is another chemical element that 
combines somewhat easily with oxygen but at a much higher temperature. 
The rest of the match head is made up of red lead, niter, or some other sub- 
stance that will release oxygen, and some glue or gum to bind the materials 
together. The heat caused by the friction of the match head against the 
striking surface is enough to cause the phosphorus to ignite; this in turn 
ignites the sulphur; and finally the wood of the match, composed largely 
of the element carbon, is lighted and oxidized. If we could take out the 
different chemical elements of which the match is formed and oxidize them 
separately, we should find that the amount of heat needed to start the oxi- 
dation of the substances would vary greatly. 

Slow Oxidation. — Oxidation may take place slowly, as seen 
in the rusting of an iron nail. If the rust and nail are weighed, 
the total weight will be more than the original nail. Do you see 
why ? Rust is iron oxide, and is formed by the union of iron and 
oxygen. Slow oxidation of chemical compounds is constantly 
taking place in nature and is a part of the process of decay and of 
breaking down of complex materials into simpler forms. 

Heat given off as Result of Oxidation, — One of the most im- 
portant effects of oxidation lies in the fact that, when anjrthing is 
oxidized, heat is produced. This heat may be of the greatest use. 
Coal, in being oxidized, gives off heat; this heat boils the water in 
the tubes of a boiler; steam is generated, wheels of an engine 
are turned, and work is performed. The energy released by the 
burning of coal may be transformed into any kind of work power. 
Energy is the ability to perform ivork. We shall find later that the 
oxidation of certain materials in the bodies of plants or animals 
releases energy. The heat of the human body is maintained by 
constant slow oxidation of food materials within the body. 

The Composition of Water. — If an electric current is passed 
through water by means of the apparatus shown in the Figure 
on the next page, the water separates into two gases, one of which 
occupies twice as much space as the other in the tubes. If we 
test the gas present in smaller quantity, we find it to be oxygen. 
The other gas, colorless, tasteless, and odorless hke the oxygen, 



10 THE ENVIRONMENT OF LIVING THINGS 




differs from it by igniting with a slight explosion when a burning 
match or spUnter is introduced in it. As it burns, drops of water 

are formed, showing 
that it is passing back 
to its original condi- 
tion, that is, it is unit- 
ing with oxygen to 
form water. This gas 
is hydrogen (hi'dro- 
jen). Hydrogen has a 
great chemical affinity 
or liking for other ele- 

Apparatus for separating water into hydrogen ^lents, hence it is USU- 
H and oxygen O: c, copper wire; p, platinum wire 

soldered to the copper, with insulation so that no ally found m nature 
copper is exposed in this tube A few drops of combined with Other 
sulphuric acid should be added to the water, to . . 

facilitate the action of the electric current. elements, aS with_ Oxy- 

gen in water. 
The Composition of the Soil. — The covering of the earth was 
probably very different in former ages from what it is now. Its 
molten plastic mass after cooling formed rock. This rock, by the 
work of the wind, frost, heat, water, and plants, has in part been 
broken into small bits. This is inorganic soil, as sea sand and 
gravel, formed usually of several elements found in rocks, such 
as caFcium, sodimn, magne'sium, siFicon, potas'sium, and iron, 
all combined with oxygen. 

A visit to the woods or to a well-kept garden shows us that there 
is another kind of soil than the inorganic soil just mentioned. This 
is the rich, dark soil containing hu'mus. Humus is made up largely 
of dead organic matter, the decayed remains of plants and ani- 
mals. If we could test the chemical elements to be found in 
humus, we should find nitrogen, hydrogen, oxygen, and also 
carbon, an important element found in all organic matter. 

Carbon. — Carbon is found in many conditions in nature. It 
is found in the bodies of plants and animals, and in coal (fossil 
plants), and it exists in a nearly pure state in the diamond. The 
presence of carbon can usually be detected by partly burning or 
charring a substance; the carbon, if present, remains as a black 
substance without taste or odor. Carbon may be collected by 



OXIDATION OF CARBON 



11 



allowing a candle flame to burn in contact with the under side 
of a sheet of glass. The black deposit is almost pure carbon. 

Oxidation of Carbon and its Result. — If we burn a candle in 
a closed jar containing air, the flame soon begins to flicker, and 
then goes out. If the cover of the jar is carefully removed, and 
a burning match lowered into the jar, the match will at once go 
out, showing the presence of a gas heavier than air which will not 
support a flame. Nitrogen of course is present, but we shall make a 
test for another gas, — a test to which nitrogen will not respond. 
If we pour into the jar a few spoonfuls of limewater,^ a colorless 
liquid, and shake it up with the gas in the jar, the lime water turns 
milky in color. This is a test for a compound known as carbon 
dioxide, which was evidently formed by the union of the carbon 
of the candle with the oxygen of the air in the jar. 

All organic or living substances, when oxidized, form carbon 
dioxide besides giving off water vapor. That oxidation of car- 
bon takes place within our own bodies may easily be 
proved by exhaling through a clean glass tube into some 
limewater ; and that water vapor is given off, by breath- 
ing against a clean, dry glass. The heat of the human 
body (98.6° F.) is the result of 
oxidation taking place within the 
body. The heat given off from 
oxidation of wood or coal in a 
stove is determined by the supply 
of oxygen we allow to pass to the 
burning material. If we open the 
draft, allowing more oxygen to 
get to the fire, we increase the heat by more rapid oxidation; 
if we shut off the oxygen supply, we decrease the amount of 
oxidation. 

Problem. Are mineral matter and water present in living things f 
{Laboratory Manual, Prob. II; Laboratory Problems, Probs. 
30, 31.)^ 

1 Limewater can be made by shaking up a piece of quicklime the size of your 
fist in about two quarts of water. Filter or strain the limewater into bottles, 
and it is ready for use. 

2 See notes on page 6. 







Oxygen Jn the air 



32 



3 



Diagram of combustion or rapid 
oxidation in a stove. 



12 THE ENVIRONMENT OF LIVING THINGS 

(a) Mineral matter, 
(h) Water. 

Mineral Matter in Living Things. — If a piece of wood is burned 
in a very hot fire, the carbon in it will all be consumed, and 
eventually nothing will be left except a grayish ash. This ash is 
seen after a wood fire in the fireplace, or after a bonfire of dry 
leaves. It consists of mineral matter which the plant has taken 
up from the soil dissolved in water, and which has been stored in 
the wood or leaves. All living things contain small quantities 
of mineral substances. 

Water in Living Things. — Water forms an important part of 
the substance of plants and animals. This is easily seen by 
weighing a number of green leaves, placing them in a hot oven for 
a few moments, and then reweighing. The same experiment made 
with a soft-bodied animal, as the oyster, would show the presence 
of even more water than in leaves. Some jellyfish are over 90 
per cent water. About 65 per cent of the human body is 
water. 

Gases Present. — Some gases are found in a free state in the 
bodies of plants or animals. Oxygen is of course present wherever 
oxidation is taking place, as is carbon dioxide. Other gases may 
be present in minute quantities. 

Problem. What foods do living organisms need? (Laboratory 
Manual, Prob. Ill; Laboratory Problems, Probs. 26, 27, 28, 29.) 

Composition of Living Matter. — The living part of a plant or 
animal is made up of the elements carbon, hydrogen, oxygen, and 
nitrogen, with a very minute amount of several other elements, 
which collectively we may call mineral matter. The living part 
of a plant corresponds closely in chemical composition to the living 
part of an animal. The starch found in grains or roots of plants 
has nearly the same chemical formula as the animal starch found 
in the liver of man; the oils of nuts or fruits are of a composition 
closely allied to the fat in the body of an animal. These and other 
building materials of a plant or animal may be placed in the three 
following groups of substances: carbohydrates (car-bo-hi'drats), 
materials containing a certain proportion of carbon, hydrogen, 
and oxygen; fats and oils, which contain chiefly hydrogen and 



FOODS 13 

carbon with less oxygen; and nitrogenous (ni-troj'e-nus) sub- 
stances, or proteins (pro^te-inz), which contain nitrogen in ad- 
dition to the above-mentioned elements. The above three kinds 
of organic materials also form a large part of the foods of all 
animals and plants. 

Foods. — What is a food ? We know that if we eat a suitable 
amount of proper foods at regular times, we shall be able to go on 
doing a certain amount of work, both manual and mental. We 
know, too, that day by day, if our general health is good, we may 
be adding weight to our bodies, and that added weight comes as 
the result of taking food into the body. A similar statement may 
be made with reference to plants and foods. If food is supplied 
in proper quantity and proportion, plants will live and grow; if 
the food supply is cut off, or even greatl}^ reduced, they will 
suffer and may die. From this, the definition which follows is 
evident. Food is any material ivhich repairs or builds up the body 
of a plant or animal, or, when oxidized in the body, furnishes it 
with energy. 

Nutrients. — Organic food substances are called nu'trients ; 
they may be classed into a number of groups, each of which 
may be detected by means of a chemical test. Such groups of 
nutrients are carbohydrates, fats and oils, and proteins. 

Carbohydrates. — Starch and sugar are common examples of 
this group of substances. The former we find in our cereals, bread, 
cake, and most of our vegetables. Several kinds of sugar are 
commonly used as food; for example, cane sugar, beet sugar, and 
glucose or grape sugar. Glucose, found as the natural sugar of 
grapes, honey, and fruits, is manufactured commercially^ by pour- 
ing sulphuric acid over starch. It is used as an adulterant for 
many kinds of foods, especially in sirups, honey, and candy. 

Test for Starch. — If we shake up a piece of laundry starch in 
water, in a test tube, and then add to the mixture two or three 
drops of iodine solution,^ we find that the particles of starch in 
the test tube turn purple or deep blue. It has been discovered 
by experiment that starch, and no 'other known substance, will be 

^ Iodine solution is made by simply adding a few crystals of the element iodine 
to 95 per cent alcohol; or, better, take by weight 1 gram of iodine crystals, f 
gram of iodide of potassium, and dilute to a dark brown color in weak alcohol 
(35 per centi or distUled water. 



14 THE ENVIRONMENT OF LIVING THINGS 



+n= 



KJ 



Test for~ starch. 



turned purple or dark blue by iodine. Therefore, this has come 

to be used as a test for the presence of starch. 

Test for Grape Sugar. — Place in a test tube the substance 

to be tested and heat it in a Uttle 
water so as to dissolve the sugar. 
Add to the fluid twice its bulk of 
Fehling's solution ^ which has been 
previously prepared. The mixture 
should now have a blue color, in 
the test tube. When heated, if gi-ape 
sugar is present in considerable quan- 
tity, the contents of the tube will 
turn first a greenish, then a yellow, 
and finally a brick-red color. Smaller 
amounts will show less decided red. 

No other substance than grape sugar will give this reaction. 
Fats and Oils. — Fats and oils form 

an important part of 'the composition 

of plants and animals. Examples of 

food in the form of fat are butter and 

cream, the oils from nuts, olives, and 

other fruits, and fat from animals. 
Test for Fats and Oils. — The 

characteristic " grease spot " is an 

easy way of determining if a sub- 
stance has fat or oil in it. If the 

substance is a fluid, pour a little of 

it on white paper; or if it is a solid, 

rub it a few times on the paper. 

Then hold the paper to the light. A 

translucent spot indicates the pres- 
ence of fat or oil. A more scientific 

test is to mash the substance to be tested, place it in an evapo- 

^ To make Fehling's solution (so-called after its discoverer), add to 35 grams of 
copper sulphate (blue vitriol) 500 c.c. of water. Put aside until it is completely 
dissolved. Call this solution No. 1. 

To 160 grams of caustic soda and 173 grams of Rochelle salt add 500 c.c. of 
water. Call this solution No. 2. 

For use mix equal parts of solutions 1 and 2. 




Test for grape sugar. 



FOODS 



15 






kJ 



rating dish, and then pour ether over it. If fat is present the 
ether will dissolve it and upon evaporation of the ether the fat 
will remain in the dish. 

Proteins. — Nitrogenous foods, or proteins, contain the element 
nitrogen in addition to carbon, hj^drogen, and oxygen of the car- 
bohydrates and fats and oils. They include some of the most 
complex substances known to the chemist, and, as we shall see, 
have a chemical composition very near to that of living matter. 
Proteins cJccur in many different substances. White of egg, lean 
meat, beans, and peas are examples of substances composed largely 
of proteins. 

Tests for Proteins. — Place in a test tube the substance to be 
tested ; for example, a bit of hard-boiled egg. Pour over it a little 

strong (80 per cent) nitric acid. Note 

the color that appears — a lemon 
yellow. If the egg is washed in water 
and a little ammonium hj^lrate added, 
the color changes to a deep orange. 
This shows that a protein is present. 

If the substance is in a liquid state, 
the presence of protein may some- 
times be proved by heating, for when 
it coagulates or thickens, as does the 
white of an egg when boiled, protein 
in the form of an alhu'men is present. 

Another characteristic protein test 
easily made at home is burning the 
substance thought to contain it. If 
the odor of burning feathers or leather Test for protein. 

is given off, then protein forms part of its composition. 

Proteins occur in several different forms, but the preceding tests 
will cover the cases most commonly met. 

Inorganic Foods. — Water and various salts, some of which, 
as lime, may be found in drinking water, form important parts in 
the diet of plants and animals. Later we shall see that green 
plants, although they use precisely the same foods (carbohydrates, 
oils, and proteins) as we do, take into their bodies the chemical 
elements from which these are formed. From these raw food 



NITRIC 
ACID 



+ 




AMMONIUM 
HYDRATE 



16 THE ENVIRONMENT OF LIVING THINGS 

materials, organic foods are manufactured in the body of the 
plant. 

Summary. — This chapter has shown us that the factors of the 
environment for both plants and animals are the same. Both use 
the chemical elements in air, water, and food in building their 
bodies or in releasing energy through oxidation of food materials. 
Both plants and animals are affected by the forces of nature 
which form part of their natural environment. It will be the work 
of future chapters to explain how. 

Problem Questions. — 1. What is the physical environment 
of a living thing? 

2. ^ATiat is an element? a compound? How is a compound 
formed ? 

3. Distinguish between rapid and slow oxidation. For what 
purposes is food used by plants and animals? 

4. What are nutrients? Explain. 

5. What is the general pm-pose of this chapter? 

Problem and Project References 

Averj^ and Sinnott, First Lessons in Physical Science. American Book Company. 

Broadhurst, Home and Coynynunity Hygiene, Chapter III. J. B. Lippincott Co. 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Martin, Human Body (Advanced Course), Revised, Chapter XXX. Henry Holt 
and Company. 

Sedgwick and Wilson, General Biology, Chapters II, III. Henry Holt and Com- 
pany. 

Sharpe, A Laboratory Manual for the Solution of Problems in Biology. American 
Book Company. 



III. THE FUNCTIONS AND COMPOSITION OF 
LIVING THINGS 

Problem. An introduction to the nature and work of living 
organisms. (Laboratory Manual, Proh. IV; Laboratory Prob- 
lems, Probs. 1, 17, 18.) 

(a) A living plant. 

(6) A living insect. 

A Living Plant and a Living Animal Compared. — A walk into 
the fields or a vacant lot on a day in tbe early fall will give 
us first-hand acquaintance with many 
common plants which, because of their 
ability to grow under unfavorable con- 
ditions, are called weeds. Such plants — 
the dandelion, butter and eggs, the shep- 
herd's purse — are particularly well fitted 
by nature to produce many of their kind 
and by this means drive out other plants 
which do not multiply so fast. On these 
and other plants we find feeding several 
kinds of animals, chiefly insects. 

If we attempt to compare, for exam- 
ple, a grasshopper with the plant on which 
it feeds, we see several points of likeness 
and difference at once. Both plant and 
insect are made up of parts, each of which, 
as the stem of the plant or the leg of the 
insect, appears to be distinct, but which 
is a part of the whole living plant or animal. Each part of the 
living plant or animal which has a separate work to do is called 
an organ. Plants and animals are spoken of as or^ganisms be- 
cause they are made of organs. 

Functions of the Parts of a Plant. — We are all familiar with 
the parts of a plant, — the root, stem, leaves, flowers, and fruit 

17 




A weed. Notice that 
the soil is barren, yet the 
weed flourishes. Photo- 
graph by W. A. Barbour. 



18 FUNCTIONS OF LIVING THINGS 

But we may not know so much about their uses to the plant. 
Each of these structures differs from every other part, and each 
has a separate work or function to perform for the plant. The 
root holds the plant firmly in the ground and takes in water and 
mineral matter from the soil; the stem holds the leaves up to the 
light and acts as a pathway for fluids between the root and leaves; 
the leaves, under certain conditions, manufacture food for the plant 
and breathe; the flowers form the fruits; the fruits hold the seeds, 
which in turn hold young plants which are capable of reproducing 
adult plants of the same kind. 

The Functions of an Animal. — If we examine the grass- 
hopper more carefully, we find that it has a head, a jointed 
body composed of a middle and a hind part, three pairs of 
jointed legs, and two pairs of wings. Obviously, the wings and 
legs are used for locomotion; a careful watching of the hind 
part of the animal shows us that breathing movements are tak- 
ing place; a bit of grass placed before it may be eaten, the tiny 
black jaws biting little pieces out of the grass. If disturbed, the 
insect hops away, and if we try to get it, it jumps or flies away, 
evidently seeing us before we can grasp it. Hundreds of little 
grasshoppers indicate that the grasshopper can reproduce its 
own kind, but in other respects the animal seems quite unlike 
the plant. The animal moves, breathes, feeds, and has sensa- 
tion, while apparently the plant does none of these. It will be 
the purpose of later chapters to prove that the functions of 
plants and animals are in many respects similar and that both 
plants and animals breathe, feed, and reproduce. 

Organs. — If we look carefully at the organ of a plant called 
a leaf, we find that the materials of which it is composed do not 
appear to be everywhere the same. The leaf is much thinner 
and more delicate in some parts than in others. Holding the 
flat, expanded blade away from the branch is a little stalk, the 
pet'iole, which extends into the blade of the leaf. Here it splits 
up into a network of tiny veins which evidently form a frame- 
work for the flat blade somewhat as the sticks of a kite hold the 
paper in place. If we examine under the compound microscope 
a thin section cut across the leaf, we shall find that the veins as 
well as the other parts are made up of many tiny boxlike units. 



ORGANS AND TISSUES 



19 




These smallest units of building material of the plant or animal 
disclosed by the compound microscope are called cells. All the 
organs of a plant or animal are built 
of these minute structures, which are 
of various sizes and shapes. 

Tissues. — The cells which form 
certain parts of the veins, the flat 
blade, or other portions of the plant, 
are often found in groups or collec- 
tions, in which the cells are more or 
less alike in size and shape. A col- 
lection of similar cells is called a 
tissue. Examples of tissues are the 
cells covering the outside of the 
human body, the muscle cells, which 
collectively allow of movement, bony 
tissues which form the framework to 
which the muscles are attached, and 
many others. 

Adaptations of Structure to Func- 
tion. — If I look at my hand as I 
write, I notice that the fingers of my 
right hand grasp the pen firmly; that because of the several 
joints in the fingers, the wrist, and forearm, free movement can 
be given to the hand when the muscles attached to the bones 
move it. The hand is capable of a great number of complicated 
and delicate movements, most of them associated with the work 
of grasping objects. Because of the peculiar fitness in the 
structure of the hand for this work, we say that it is adapted 
to this function, that is, grasping objects. Each organ of the 
plant is fitted or adapted in some way to do certain kinds of 
work. It is the object of the chapters following to point out 
how the parts of a plant or animal are adapted to their various 
functions. 



Section through a leaf, greatly 
magnified : E, cells of upper epi- 
dermis; P, palisade layer; V, 
vein; M, cells with air spaces, 
A, between them; L, cells of 
lower epidermis; S, stoma or 
mouth-like opening; g, guard 
cell. 



Problem. To discover the structure and properties of living 
matter. {Laboratory Manual, Proh. V; Laboratory Problems, 
Prob. 19.) 



20 



COMPOSITION OF LIVING THINGS 



Cells. — Living things, when viewed under a compound mi- 
croscope, are found to be made up of tiny units of structure, or 
cells, each separated from its neighbors by a very delicate 
membrane or a wall. The inside of the cell is composed of gray- 
ish semifluid matter which seems to contain innumerable granules 

of various sizes and shapes. This sub- 
stance is known as protoplasm (pro'td- 
plazm), and usually contains a struc- 
ture known as the nucleus (nti'kle-us). 
Within the nucleus are tiny bits of 
matter which, when the cell is stained 
with logwood or other dyes, take up 
the stain more readily than the sur- 
rounding material and hence are called 
chromosomes (kro'm6-somz), which 
means " color-bearing bodies. '^ A dis- 
tinction is usually made between the 
protoplasm within the nucleus and that 
within the rest of the cell body, the 
latter being called cytoplasm (si't6- 
plazm). A cell may be defined as a 
unit of structure in all living things, a 
tiny mass of living matter usually con- 
taining a nucleus. 
The cell is surrounded by a very delicate living structure 
called the cell membrane. Outside this membrane a wall is 
formed by the activity of the protoplasm in the cell. These 
cell walls, in plants, are of ceVlulose or wood. 

How Cells form Others. — A cell grows to a certain size and 
then splits into two new cells. In this process, which is of very 
great importance in the growth of both plants and animals, the 
chromosomes divide first. Each chromosome splits lengthwise 
and the parts go in equal numbers to each of two nuclei 
formed from the old nucleus. The chromosomes are believ-ed to 
be the bearers of the qualities which can be handed down from 
plant to plant and from animal to animal; in other words, the 
inheritable qualities which make the offspring like its parents. 
Lastly, a cell wall is developed dividing the cytoplasm, and two 




A typical cell, composed of 
protoplasm. The cell may be of 
almost any shape. M, cell wall 
or cell membrane; N, nucleus; 
n, nucleolus; V, vacuole; F, 
food or other substance. 



CELLS 



21 




new cells are formed. This process is known as cell division. 
It is the usual method of growth found ^ in the tissues of 
plants and animals. 

Cells of Various Sizes and Shapes. — Plant cells and animal 
cells are of very diverse shapes and sizes. There are cells so 
large that they can 
easily be seen with the 
unaided eye; for ex- 
ample, the root hairs of 
plants and eggs of some 
animals. On the other 
hand, cells may be so 
minute that, as in the 
case of the plant cells 
named bacteria, a mil- 
lion could be placed ^ . ... 

. , . , . , Stages in the division of one cell to form two 

Wltnin tniS letter O. cells. Note the separation of the chromosomes in 
The forms of cells may ^^® nucleus. Which part of the cell divides first? 

be extremely varied in different tissues; they may assume the 
form of cubes, columns, spheres, flat plates, or may be extremely 
irregular in shape. One kind of tissue cell has a body so small 
as to be quite invisible to the naked eye, although it has a pro- 
longation several feet in length. Such are some of the cells of 
the nervous system of man and other large animals, as the ox, 
elephant, and whale. 

Varying Sizes of Living Things. — Plant cells and animal 
cells may live alone or they may form collections of cells. Some 
plants are so simple in structure as to be formed of only one 
kind of cells. Usually living organisms are composed of several 
groups of different kinds of cells. The size of the cells does not 
seem to bear any relation to the size of the organism, but larger 
organisms are made up of more cells. The human body, for ex- 
ample, is composed of untold millions of cells, while some simple 
plant or animal m-ay be composed of a very few cells or even 
a single cell. 

Relation to Organic and Inorganic Matter. — The cells of 
which we have been speaking are examples of organic matter. 
They live and grow and in doing so make use of the inorganic 



22 COMPOSITION OF LIVING THINGS 

matter covering the earth, as air, water, and soil. Plants and ani* 
mals make their homes in earth, air, or water; they take in the 
oxygen of the atmosphere; they take in water; but in the main 
the food of animals consists of organic matter. Green plants, 
on the other hand, manufacture most of their food out of the 
inorganic matter contained in the soil, air, and water, and then 
change this food into the hving matter of their own bodies. 
This organic matter in turn may become food for animals. 

Chemical Composition of Protoplasm. — Living matter, when 
analyzed by chemists in the laboratory, seems to have a very 
complex chemical composition. It is somewhat like a protein in 
that it always contains the element nitrogen. It also contains 
the elements carbon, hydrogen, oxygen, and a little sulphur. 
Calcimn, iron, silicon, sodium, potassium, phosphorus, and other 
mineral matters are usually found in very minute quantities in 
its composition. We believe that the matter out of which plants 
and animals are formed, although a very complex building ma- 
terial and almost impossible of correct analysis, is composed of 
the above-named elements. What is of far more importance to 
us is the fact that it is distinguished by certain properties which 
it possesses and which inorganic matter does not possess. 

Properties of Protoplasm. — The properties of protoplasm are 
as follows : — • 

(1) It is irritable: it responds to influences or stimuli which 
come to it from outside its own substance. Both plants and 
animals are sensitive to touch or stimulation by light, heat, or 
electricity. Green plants turn toward the source of light. 
Some animals are attracted, and others are repelled by light. 

(2) Protoplasm has the power to move and to contract. Mus- 
cular movement is a familiar instance of this power. Plants 
move their leaves and other organs. 

(3) Protoplasm can take in, digest, and make food over into its 
own substance. This process is known as nutrition. As a result 
of this process the organism grows. 

(4) Protoplasm, be it in the body of .a plant or of an animal, 
uses oxygen. It breathes. Thus substances taken into the body 
may be oxidized, and release energy for movement and the other 
activities of plants and animals. 



PROTOPLASM 23 

(5) Protoplasm has the power to rid itself of waste materials, 
especially those which might be harmful to it. A tree sheds its 
leaves, and as a result gets rid of the accumulation of mineral 
matter in the leaves. Plants and animals alike pass off the car- 
bon dioxide which results from the very processes of living, the 
oxidation of parts of their own bodies. Animals eliminate 
wastes containing nitrogen through the skin and the kidneys. 

(6) Protoplasm can reproduce, that is, form other matter like 
itself. New plants are constantly appearing to take the places of 
those that die. The supply of living things upon the earth is 
not decreasing; reproduction is constantly taking place. 

(7) Protoplasm has, as we shall see later, certain other physical 
properties which help explain certain functions of plants and 
animals. 

Summary. — To sum up, we find that living protoplasm has 
the properties of sensibility, motion, growth, and reproduction 
both in its simplest state as a one-celled plant or animal and when 
it enters into the composition of a highly complex organism 
such as a tree, a dog, or a man. The cells in these organisms 
have the same general structure in plants as in animals (with 
the exception of certain minor differences that we shall see 
later). Protoplasm is composed of the same chemical elements 
that are found in the air, water, soil, and in organic foods. How 
protoplasm is made from non-living matter is a wonderful story, 
a part of which we shall hear later. 

Problem Questions. — 1. Why are living things called or- 
ganisms ? 

2. Explain the terms function, adaptation, organ, tissue. 

3. Describe from the diagrams a cell and show how it divides. 

4. What is the chemical composition of protoplasm? 

5. Discuss the properties of protoplasm. 

Problem and Project References 

Atkinson> First Studies of Plant Life, Chapter XI. Ginn and Company. 

Conn, Biology, Chapters I, II. Silver, Burdett and Company. 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Sedgwick and Wilson, General Biology. Henry Holt and Company. 

Shull, Principles of Animal Biology, Chapter III. McGraw-Hill Company^ 

Sharpe, A Laboratory Manual. American Book Company. 

Stevens. Plant Anatomy, Chapter I. P. Blakiston's Sons and Company. 



IV. FLOWERS AND THEIR WORK 



Problem. The structure and work of the parts of a flower, 
{Laboratory Manual^ Proh. VI; Laboratory Problems, Probs. 

12, 21, 22.) 

Structure of a Simple Flower. — You have all seen in winter 
a branch of a tree bearing buds. It would not be difficult to 

imagine that some of the buds are 
to form branches while others 
form flowers. Such is really the 
case. A flower is a shortened 
branch made for the purpose of 
producing seeds for the plant. 
Our problem will be to learn 
something of the structure and 
uses of the parts of a very simple 
flower. The expanded portion of 
the flower stalk, which holds the 
parts of the flower, is called the 
receptacle. 

The Floral Envelope, — The 
small green leaflike parts cover- 
ing the unopened flower are called 
se'pals. All together they make 
the calyx (ka'lix). The sepals 
come out in a circle or whorl on 
the flower stalk. The more 
brightly colored structures are 
the pefals. They form the 
corol'la. The corolla is of im- 
portance, as we shall see later, in 
making the flower conspicuous. 
The Essential Organs, — A flower, however, could live with- 
out sepals or petals and still produce seeds, the work for which it 

24 




A typical flower, cut lengthwise 
to show all parts. Compare with the 
picture of a flower on page 31. R, 
receptacle; S, sepal; P, petal; St, 
stamen; Pi, pistil. The stamen con- 
sists of a stalklike filament / and a 
boxlike anther a, which holds the 
pollen. The pistil is made up of an 
enlarged ovary o, a stalk or style st, 
and a terminal stigma s. 



STRUCTURE OF A FLOWER 



25 



exists. The essential organs of the flower are within the so-called 

floral envelope. They consist of the stamens (sta'menz) and jpistily 

the latter being in the center of the flower. The stamens have 

knobbed ends and are arranged in a circle around the pistil. 

The stalk of the stamen is called the fiVament 

and the knobbed end is the an'ther, which is 

in reality a hollow box which produces a large 

number of little grains called pol'len. It is 

necessary for the reproduction of new plants 

that the pollen grains get out of the anther. 

Each pistil is composed of a rather stout base 

called the o'vary, containing the o'vules which 

later may form the seeds, a stalklike structure 

called the style, and the stigma, which is the 

upper end of the style, and in some cases is 

broadened. The surface of the stigma usually 

secretes a sweet fluid in which grains of pollen 

from flowers of the same kind can grow. 

Pollen. — Pollen grains of various flowers, 
as seen under the microscope, differ greatly 
in form and appearance. Some are relatively 
large, some small, some rough, others smooth, 
some spherical, and others angular. They all 
agree, however, in having a thick wall, with a 
thin membrane under it, the whole inclosing 
a mass of protoplasm. At an early stage the 
pollen grain contains but a single cell. Later, 
however, we can distinguish two nuclei in the protoplasm. 

Growth of Pollen Grains. — Under certain conditions a pollen 
grain will germinate; that is, burst open and grow a threadlike 
projection called the pollen tube; see Figure. . Two nuclei enter 
this tube. One of them, the tube nucleus, disappears after a 
time. The second, germinative nucleus, divides to form two 
sperm nuclei. 

Fertilization of the Flower. — If we cut the pistil of a large 
flower (as a lily) lengthwise, we notice that the style appears to 
be composed of rather spongy material in the interior; the 
ovary is hollow and is seen to contain a number of rounded 




Pollen grains, in 
section; oTie is ger- 
minating. T, tube 
nucleus ; *b', sperm 
nuclei. 



HUNT. KEW ES. 3 



26 



FLOWERS AND THEIR WORK 



Pg— 



structures which appear to grow out from the wall of the ovary. 
These are the ovules. The ovules, under certain conditions, be- 
come seeds. An explanation of these conditions may be had if 
we examine, under the microscope, a very thin section of a pis- 
til on which pollen has begun to germinate. The central part 
of the style is found to be either hollow or composed of a soft 
tissue through which the pollen tube can easily grow. Upon 

germination, the pol- 
len tube grows down- 
ward through the 
spongy center of the 
style, follows the path 
of least resistance to 
the space within the 
ovary, and there en- 
ters an ovule. It is 
believed that some 
chemical influence at- 
tracts the pollen tube. 
The sperm cell pen- 
etrates an ovule by 
making its way 
through the hole made 
by the pollen tube, 
called the micropyle 
(mi'cr6-pil), and then 
grows toward a clear 
bit of protoplasm 
known as the em'hryo 
sac. The embryo sac 
is an ovoid space, 
microscopic in size, 
filled with semifluid 
protoplasm containing several nuclei. (See Figure.) One of the 
nuclei, with the protoplasm immediately surrounding it, is called the 
egg cell. It is this cell that the sperm cell of the pollen tube grows 
toward; ultimately the sperm cell reaches the egg cell and unites 
with it. The union of the nucleus of the sperm cell with the nucleus 




A flower cut lengthwise to illustrate fertiliza- 
tion: pg, germinating pollen grain which forms a 
pollen tube pt and grows down through the spongy 
style and through the micropyle m into the em- 
bryo sac within the ovary o. The sperm nucleus 
s is about to unite with an egg nucleus e to form 
a fertilized egg. 



CROSS-POLLINATION 27 

of the egg cell in the ovary is known as fertilization. The single 
cell formed by the union of the sperm cell and the egg cell is 
now called a fertilized egg. 

When the two cells unite to form a fertilized egg, this egg, 
by constant divisions of the cells, forms an embryo or baby 
plant. This is contained in the seed and, as we know, will de- 
velop into an adult plant if given proper environmental con- 
ditions. 

Problem. A study of cross-pollination and some means of 
bringing it about. (Laboratory Manual, Prob. VII; Laboratory 
Problems, Probs. 13, 14, 15.) 

(a) Adaptations in the flower. 

(b) Adaptations in an insect agent. 

(c) Other agents. 

History of the Discoveries regarding Pollination of Flowers. 

— Although the ancient Greek and Roman naturalists had some 
vague ideas on the subject of fertilization, it was not until the 
latter part of the eighteenth century that it was demonstrated 
that pollen is necessary for the growth of the embryo within 
a seed. In the latter part of the eighteenth century a book ap- 
peared in which a German named Conrad Sprengel worked out 
the facts that the structure of certain flowers seemed to be 
adapted to the visits of insects. Certain facilities were offered 
to an insect in the way of easy foothold, sweet odor, and es- 
pecially food in the shape of pollen and nectar, the latter a 
sweet-tasting substance manufactured by certain parts of the 
flower known as the nectar glands. Sprengel further discov- 
ered the fact that pollen could be and is carried by the insect 
visitors from the anthers of the flower to its stigma. It was 
not until the middle of the nineteenth century, however, that 
an Englishman, Charles Darwin, worked out the true relation 
of insects to flowers by his investigations upon the cross-pollina- 
tion of flowers. By pollination we mean the transfer of pollen 
from an anther to the stigma of a flower. Self-pollination is the 
transfer of pollen from the anther to the stigma of the same flower; 
cross-pollination is the transfer of pollen from the anthers of one 
fl,ower to the stigma of another flower of the same hind. Many 



28 



FLOWERS AND THEIR WORK 



species of flowers are self-pollinated and do not do as well in 
seed production if cross-pollinated, but Charles Darwin found 
that some flowers which vs^ere self-poflinated did not produce as 
many seeds, and that the plants which grew from their seeds 
were smafler and weaker than plants from seeds produced by 
cross-polhnated flowers of the same kind. He also found that 
plants grown from cross-polKnated seeds tended to vary more 
than those grown from self -pollinated seed. This has an im- 
portant bearing, as we shall 
see later, in the production 
of new varieties of plants. 
Microscopic examination of 
the stigma at the time of 
pollination also shov/s that 
the pollen from another 
flower germinates more quick- 
ly than the pollen which has 
fallen from the anthers of the 
same flower. This latter fact 
in most cases renders it 
unlikely for a flower to pro- 
duce seeds by its own pollen. 
Darwin worked for many 
years on the pollination of 
many insect- visited flowers, 
and discovered in almost 
every case that showy, sweet- 
scented, or otherwise attrac- 
tive flowers were adapted or 
fitted to be cross-polHnated 
by insects. He also found that, in the case of flowers that 
were inconspicuous in appearance, often a compensation ap- 
peared in the odor which rendered them attractive to certain 
insects. The so-called carrion flowers, pollinated by flies, are 
examples, their odor being like that of decayed flesh. Other 
flowers, which open at night, are white and provided with a 
powerful scent so as to attract night-flying moths and other 
insects. Flowers adapted to be cross-pollinated by insects are 




A wild orchid, a flower of the type 
from which Charles Darwin worked out 
his theory of cross-pollination by insects. 



CROSS-POLLINATION 



29 



frequently irregular in shape. Thus butter and eggs is a flower 
which is well fitted for cross-pollination by insects. 

Suggestions for Field Work. — At this point, at least one field trip 
should be introduced for the purpose of studying under natural conditions 
the cross-polhnation of flowers by insects. Directions for a field trip will 
be found in Hunter's Laboratory Problems in Civic Biology, pages 39-43. 

Insects as Pollinating Agents. — No one who sees a hive of 
bees with their wonderful communal life can fail to realize that 
these insects play a great part in the life of the flowers near the 




The bee is adapted for carrying pollen. How? A, dorsal view of bee; B, front 
view of head; m, mouth parts; C, a leg, showing the pollen basket p. Note the 
feathery hairs on the upper joints of the leg. 

hive. A famous observer named Sir John Lubbock tested bees 
and wasps to see how many trips they made daily from the hive 
to the flowers, and found that the wasp went out on 116 visits 
during a working day of 16 hours, while the bee made almost 
as many visits, and worked only a little less time than the wasp 
worked. It is evident that in the course of so many trips to 
the fields a bee must light on and cross-pollinate many hundreds 
of flowers. 

Study of a Bee. — The body of a bee (and of all other insects) 
is divided into three parts. Attached to the middle part (the 



30 FLOWERS AND THEIR WORK 

tho'rax) are three pairs of jointed legs and two pairs of tiny- 
wings. By the legs and the jointed body Ave are able to dis- 
tinguish insects from other animals. If we look closely at the 
bee, we find the body and legs more or less covered with tiny 
hairs; especially are these hairs found on the legs. When a plant 
or animal structure is fitted to do a certain kind of work, we say it 
is adapted to do that work. The joints in the leg of the bee adapt 
it for complicated movements; the arrangement of stiff hairs along 
the edge of a concavity in one of the joints of the leg forms 
a structure well fitted to hold pollen. In this basket pollen is col- 
lected by the bee and taken to the hive to be used as food. But 
while gathering pollen for itseK, the bee catches pollen on the hair 
and other projections on its body and legs and carries it from 
flower to flower. Thus cross-pollination may be effected. 

Pollination not intended by the Bee. — The cross-pollination 
of flowers is not planned by the bee; it is simply an incident in 
the course of the food gathering. The bee visits a large number 
of flowers of the same species during th^ course of a single trip 
from the hive, and it is then that cross-pollination takes place. 

Suggestions for Field Work. — In any locality where flowers are abun- 
dant, try to answer the following questions: Plow many bees visit the lo- 
caUty in ten minutes? How many other insects alight on the flowers? Do 
bees visit flowers of the same kind in succession, or fly from one flower on 
a given plant to another on a plant of a different kind? If the bee alights 
on a flower cluster, does it visit more than one flower in the same cluster? 
How does a bee alight? Exactly what does the bee do when it alights? Try 
to decide whether color or odor has the most effect in attracting bees to 
flowers. Sir John Lubbcck tried an experiment which it would pay a num- 
ber of careful pupils to repeat. He placed a few drops of honey on glass 
slips and placed them over papers of various colors. In this way he found 
that the honeybee, for example, could evidently distinguish different colors. 
Bees seemed to prefer blue to any other color. Flowers of a yellow or flesh 
color were preferred by flies. It would be of considerable interest for some 
student to work out this problem with our native bees and with other 
insects. Test the keenness of sight in insects by placing a white object (a 
white golf ball will do) in the grass and see how many insects will alight 
on it. Try to work out some method by which you can decide whether a 
given insect is attracted to a flower by odor alone. 

The Sight of the Bumblebee. — The large eyes located on the 
sides of a bee's head are made up of a large number of little units, 



CROSS-POLLINATION 



31 



each of which is considered 
to be a very simple eye. The 
large eyes are therefore called 
the compound eyes. All insects 
are provided with compound 
eyes, with simple eyes, or, in 
most cases, with both. The 
simple eyes of the bee may 
be found by a careful ob- 
server between and above 
the compound eyes. 

One would suppose that 
with so many eyes the sight 
of insects would be extremely 
keen, but such does not seem 
to be the case. Insects can, 
as we have already learned, 
distinguish differences in color 
at some distance; they can 




Front view of the head of a fly. The 
compound eyes are at the sides. Photo- 
graph from American Museum of 
Natural History, New York. 



see moving objects, but they do not seem to be able to make 
out form well. To make up for this, they appear to have an 

extremely well-developed sense 
of smell. Insects can distin- 
guish at a great distance odors 
which to the human nose are 
imperceptible. Night-flying in- 
sects, especially, find the flow- 
ers by the odor rather than by 
color. 

Nectar and Nectar Glands. — 
The bee is attracted to a flower 
fcr food. This food may consist 
of pollen or nec'tar. Nectar is 
a sugary solution that is formed 
in the flower by little collec- 
tions of cells called the nectar 
A my: p petal; .-S stamen (anther); glands. The nectar glands are 

bEP, sepal; St, pistil (stigma). No- ^ ^ 

tice the nectar guides ou the petals. USUally SO placed that tO reach 




32 



FLOWERS AND THEIR WORK 



them the insect must first brush the stamens and pistil of the 
flower. Frequently the location of the nectaries (nectar glands'! 
is made conspicuous by brightly colored markings on the corolla 
of the flower. The row of dots in the tiger lily is an example. 

Mouth Parts of the Bee. — The mouth of the bee is adapted to 
take in the foods we have mentioned, and is used in this way, for 
the same purposes that a man would use the hands and fingers. 
The honeybee laps or sucks nectar from flowers, it chews the pollen, 
and it uses part of the mouth as a trowel in making the honey- 
comb. A glance at the Figure, page 29, shows us that the mouth 
parts of the bee are complex. The parts consist of a pair of 

very small jaws or mandibles, 
certain other structures, max- 
il'lcBj part of the lower lip 
called the labial palps, and 
a long tongue-like structure 
called the lig'ula. The uses 
of the mouth parts may be 
made out by watching a bee 
on a well-opened flower. 

Other Flower Visitors. — 
Other insects besides the bee 
are pollen carriers for flowers. 
Among the most useful are 
moths and butterflies. Both 
of these insects feed only on 
nectar, which they suck 
through a long tubelike pro- 
boscis (pro-bos'is). The heads 
and bodies of these insects 
are more or less thickly cov- 
ered with hairs, and the wings 
are thatched with tiny hairlike scales. Ah these structures are 
of some use to the flower because the}^ collect and carry pollen; 
but the palp, a fluffy structure projecting from each side of the 
head of a butterfly, collects a large amount of pollen, which 
is deposited upon the stigmas of other flowers when the butterfly 
pushes its head down into the flower tube after nectar. 




Long-billed humming birds: above, one 
at rest; below, one gathering nectar. 
Photograph from American Museum of 
Natural History. 



CROSS-POLLINATION 



33 



Flies and a few other insects are agents in cross-pollination. 
Humming birds (picture, p. 32) are also active agents in some 
flowers. Snails are said in rare instances to carry pollen. Man 
and the domesticated animals pollinate a few flowers by brush- 
ing past them through the fields. 

Butter and Eggs. — From July to October butter and eggs, a 
very abundant weed, may be found especially along roadsides and 
in sunny fields. It bears a tall and conspicuous flower cluster 
known as a spike, the yellow and orange flowers being arranged 
so that they come out directly from the main flower stalk^ 

The corolla projects into a spur on the lower side; an upper 
two-parted lip shuts down upon a lower three-parted lip. The 
four stamens are in pairs, two long and two short. 

Certain parts of the corolla which are more brightly colored than 
the rest of the flower, serve as a guide to insects. This flower is 
visited most frequently by bumble- 
bees, which are guided by the orange 
lip to alight just where they can push 
their way into the flower. The bee, 
seeking the nectar secreted in the spur, 
brushes its head and shoulders against 
the anthers. On visiting another flower 
of the cluster, it would be an easy 
matter accidentally to transfer this 
pollen to the stigma of that flower. In 
this way cross-pollination is effected. 

Insects may also cause self-pollina- 
tion by rubbing against the upper pair 
of stamens, thus depositing some pol- 
len on the stigma as they back out of 
the flower. 

Cross-pollination of a Head (Clover). — In a head, which is 
a closely massed cluster of little flowers, as the clover, cross- 
pollination is usually effected by bumblebees which rapidly work 
from one flower to another in the same group, inserting their 
tongues deep into the flower cups. 

Cross-pollination of a Composite Head. — The composite head is 
made clear by a daisy, aster, or sunflower. This head has an 




Cross-pollination of butter 
and eggs by a bumblebee: A, 
anther; S, stigma; N, nectar 
spur. 



34 



FLOWERS AND THEIR WORK 



outer circle of green parts which look like sepals, but in reality- 
are a whorl of leaflike parts. Taken together these form an 





Composite head. Photograph of gail- 
lardia by Albert E. Butler, from Ameri- 
can Museum of Natural Historic New 
York. 



Section of daisy; a composite 
head. R, ray flower; D, disk flow- 
er; /, involucre; s, stigma; a, an- 
thers; 0, ovary. 

involucre (in'vo-lu-ker). In- 
side the involucre is a whorl 
of brightl}^ colored, irregular 
flowers called the ray flowers. 
Thej^ appear to act, in some 
instances at least, as an at- 
traction to insects by show- 
ing a definite color (see the common dogwood). The flowers 
occupying the center of the cluster are the disk flowers. Pollen 

is carried easily from one flower to 
another even by an insect which crawls. 

Adaptations to prevent Self-pollination. 
— In some flowers, as is shown by the 
primulas of our hothouses, the stamens 
and pistils are each of two different 
lengths in different flowers. Short styles 
and long or high-placed filaments are 
found in one flower, and long styles with 
short or low-placed filaments in another. 
Pollination is most likely to be effected 
b}^ some of the pollen from a low-placed 
anther reaching the stigma of a short- 
styled flower, or by the pollen from a 
high anther being placed upon a long- 
Flowers which have this pe- 




Section of dandelion, 
showing two flowers: h, 
colored leaflike bract sur- 
rounding the flower; st, 
stigma; s, style; a, 
anthers; o, ovary. What gtyjed pistil 
makes the dandelion head 



conspicuous i 



culiar condition are said to be dimorphic 



CROSS-POLLINATION 



35 




Stamens (light) and pistils (dark), and course 
of cross-pollination in loosestrife, a trimorphic 
flower. 



(Greek = of two forms). There are, as in the case of the 
loosestrife, trimorphic flowers, having pistils and stamens of 
three lengths. 

In many kinds of 
flowers we find that 
the stamens ripen be- 
fore the pistils, or just 
the opposite may hap- 
pen. Such a condition 
effectually prevents 
self-pollination. This 
condition is called di- 
chogamy (dl-c6g'a-mi). 

Other examples. 
Many other examples 
of adaptations to secure cross-pollination by means of the visits 
of insects might be given. The mountain laurel, which makes 
our hillsides so beautiful in late spring, shows a remarkable 
adaptation in having the stamens caught in little pockets of 
the corolla. The weight of the visiting insect on the corolla 
releases the anther of the stamen from the pocket in which it 
rests, the anther opens, and the body of the visitor 
is dusted with pollen. 

Still another example of cross-pollination is 
found in the yucca, a desert-loving semitropical 
lily. In this flower the stigma is above the anther, 
and the pollen is sticky and could not be trans- 
ferred except by insect aid. A little moth, called 
the pro'nuba, gathers pollen from an anther, flies 
away with this load to another flower, there deposits 
eggs in the ovary of the pistil, and then rubs its 
load of pollen over the stigma of the flower. The 
young hatch out and feed on some of the young 
nating pistil of seeds which have been fertilized by the pollen placed 
yucca. on the stigma by the mother, and then bore out of 

the seed pod and escape to the ground, 'leaving the plant to 
develop the remaining seeds without further molestation. 
The pollination of the fig shows another wonderful example 




36 FLOWERS AND THEIR WORK 

of adaptation The fig" is not a fruit but a cluster of fruits, 
growing inside the inturned ends of a fleshy flower stalk. There 
may be three kinds of flowers in the clusters, some bearing 
stamens only, some with pistils only with long styles, and others 
with' short styles. Some fig flower clusters have long-styled 
pis'tillate flowers only, others contain both short-styled and 
stam'inate flowers, the latter above the pistillate flowers. All 
of these flowers are visited by a Httle wasp. When it visits the 
short-styled and staminate fig it lays its eggs in the ovary, which 
it can easily reach with its egg-depositing organ (the ovipositor). 
The females which hatch work their way out and in doing so 
inrush against the staminate flowers, thus coUecting poUen on 
their bodies. They then seek other figs in order to lay their 
eggs. If a wasp reaches another short-styled flower cluster the 
eggs are laid and development takes place as before. But if it 
flies to a long-styled cluster it cannot reach the ovary to deposit 
its eggs. In both cases, however, the wasp has carried poUen to 
the stigma and pollination takes place with the subsequent 
development of seeds. The figs we eat are the ones developed 
from the long-styled pistillate flowers. 

Pollination by the Wind. — Not aU flowers are dependent 
upon insects for cross-pollination. Many of the earliest spring 
flowers appear almost before the insects do. In many trees, 
such as the oak, poplar, and maple, the flowers open before 
the leaves come out. Such flowers are dependent upon the 
wind to carry the pollen from the stamens of one flower to the 
pistil of another. 

Among the adaptations that a wind-poUinated flower shows 
are: (1) The development of very many pollen grains to each 
ovule. In one of the insect-pollinated flowers, that of the night- 
blooming cereus, the ratio of pollen grains to ovules is about 
eight to one. In flowers which are to be pollinated by the wind, 
a large number of the poUen grains never reach their destina- 
tion and are wasted. Therefore in these plants several thou- 
sands, perhaps hundreds of thousands, of pollen grains will be 
developed to every ovule produced. Such are the pines. In 
May and early June the ground under pine trees is often yellow 
with pollen, and the air is filled with the pollen dust for miles 



CROSS-POLLINATION 



37 



from the trees. The same is true, also, with many of the 
grasses, including corn or maize. 

(2) The anthers are usually held high and exposed to the 
wind when ripe. The common plantain and timothy grass are 
excellent examples. 




Cross-pollination of com by the wind. 



(3) The pistil of the flower is pecuHarly fitted to retain the 
pollen by having feathery projections along the sides which 
increase the surface of the stigma. This can be seen in 
grasses. In the Indian corn the stigma is the so-called silk 
which protrudes beyond the covering of modified leaves which 
form the husk of the ear of corn. All our grains, wheat, rye, 
oats, and others, have the typical feathery pistil of the wild 
grasses from which they have been developed. 

(4) The corolla is often entirely lacking. It would only be 
in the way in flowers that are dependent upon the wind to carry 
pollen. 

Imperfect Flowers. — Some flowers, the wind-poUinated ones 
in particular, are imperfect; that is, they lack either stamens or 
pistils. In such flowers, cross-pollination must of necessity be 
depended upon. If only stam'inate flowers (those which con- 
tain only stamens) are developed on one plant, and only 



38 



FLOWERS AND THEIR WORK 



pis'tillate flowers (those which bear only pistils) on another, 
we call the species dioecious (di-e'shus). A common example 

is the willow. 




a- 




Other species have staminate 
and pistillate flowers on the 
same plant. In this case they 
are said to be monoecious (m(5- 
ne'shus). The oak, hickory, 
beech, birch, walnut, and 
chestnut are familiar examples. 

Protection of Pollen. — Pol- 
len, in order to be carried 
effectively by the wind, insects, 
or other agencies, must be dry. 
In some flow^ers the irregular 

Pistillate flower P, and staminate flow- form of the COrolla protects the 
er S, of the willow; h, bract; o, ovary; ^^ ^ -, <-,,i 

St, style; s, stigma; /, filament; a, anther. PoUen from dampneSS. Other 

flowers close up at night, as 
the morning-glory and four-o'clock. Still others, as the bell- 
flower, droop during a shower or at night. 

Pollen is also protected from insect visitors as ants, plant 
lice, or other small crawling insects which would carry off pollen 
but give the flower no return by cross-pollinating it, by hairs 
which are developed upon the filaments or on the corolla. 
Sometimes a ring of sticky material is found making a barrier 
around the stalk underneath the flower. Many other adapta- 
tions of this sort might be mentioned. 

Artificial Cross-pollination and its Practical Benefits to Man. 
— Artificial cross-pollination is practiced by plant breeders and 
can easily be tried in the laboratory or at home. First the 
anthers must be carefully removed from the bud of the flower 
so as to eliminate all possibility of self-pollination. The flower 
must then be covered so as to prevent access of pollen from 
without; when the pistil is sufficiently developed, pollen from 
another flower, having the characteristics desired, is placed on the 
stigma and the flower again covered to prevent any other pollen 
reaching the flower. The seeds from this flower when planted 
may give rise to plants with some characteristics of each of 



CROSS-POLLINATION 39 

the plants from which the pollen and egg cell came. Naturally 
the two plants cross-pollinated must be of the same or of closely 
allied species. If they are of different species or varieties, the 
new plants produced are called hy'hrids. It is this kind of work 
that made Luther Bur bank famous. An excellent project report 
might be made on his work by reading Harwood's New Creations 
in Plant Life. 

Summary. — In summarizing this chapter we find (1) that 
seeds are produced as a result of the fertilization of the egg cell 
by the sperm cell in the ovary of a flower; (2) this is brought 
about by pollination; (3) pollination may be self (within the 
flower) or cross (from the anthers of one flower to the stigma 
of another flower, usually of the same species) ; (4) that insects 
as well as other agents may bring this about; and (5) that there 
are many adaptations within flowers to prevent self-pollination, 
the chief of which are: 

The stamens and pistils may be found in separate flowers, either 
on the same or on different plants. 

The stamens may produce pollen before the pistil of the same 
flower is ready to receive it, or vice versa. 

The stamens and pistils may be so placed with reference to each 
other that pollination can be brought about only by outside assistance. 

Problem Questions. — 1. What is the use of a flower? 

2. What is fertilization ? How is it accomplished in a flower ? 

3. Mention some adaptation in insects to help bring about 
cross pollination in flowers. 

4. Discuss three types of adaptations to insure cross-pollina- 
tion in flowers. 

5. What are some practical benefits from cross-pollination? 

Problem and Project References 

Atkinson, First Studies of Plant Life, Chapters XXV-XXVI. Ginn and Com- 
pany. 
Dana, Plants and their Children, pages 187—255. American Book Company. 
Darwin, Orchids Fertilized by Insects. D. Appleton and Company. 
Hunter, Laboratory Problems in Civic Biology. American Book Company. 
Lubbock, Flowers, Fruits and Leaves, Part I. The Macmillan Company. 
Lubbock, British Wild Flowers. The Macmillan Company. 
Milller, The Fertilization of Flowers. The Macmillan Company. 
Sharpe, A Laboratory Manual. American Book Company. 



V. FRUITS AND THEIR USES 

Problem. A study of fruits to discover — 

(a) Their uses to a plant. 

(b) How they are scattered. 

(c) Their protection from animals and other enemies. 
(Laboratory Manual, Prob. VIII; Laboratory Problems, Probs. 

23, 21^) 

A Typical Fruit, — the Pea or Bean Pod. — If a withered 
flower of any one of the pea or bean family is examined care- 
fully it will be found that the pistil of the flower continues to 
grow after the rest of the flower withers. If we examine the 
pistil from such a flower we find that it is the ovary that has 
enlarged. The space within the ovary has become almost filled 

sti... 

sty...]) 




A, B, C, stages in the formation of fruit of pea; Z>, E, F, corresponding stages 
in apple fruit; c, calyx; p, petals; st, stamens; sti, stigma; sty, style; ov, ovary; 
/, funiculus; fr, valve of pod; s, seed. 

with a number of ovoid bodies, attached along one edge of the 
inner wall. These we recognize as the young seeds. 

The pod of a bean, pea, or locust illustrates well the growth 
from the flower. The flower stalk, the ovary, and the remains 
of the style, the stigma, and the calyx, can be found on most 

40 



A TYPICAL FRUIT 



41 



unopened pods. If the pod is opened, the seeds will be found 
fastened to the ovary wall each by a little stalk called the 
funic'ulus. That part of the ovary wall which bears the seeds 
is the jplacen'ta. The walls of the pod are called valves. 

The pod, which is in reality a ripened ovary with other parts 
of the flower attached to it, is considered a fruit. By defini- 
tion, a fruit is a ripened ovary together with any parts of the flower 
that may he attached to it. The chief use of the fruit is to hold 
and to protect the seeds; it may ultimately distribute them 
where they can reproduce young plants. 

Formation of Seeds. — Each seed has been formed as a direct 
result of the fertilization of the egg cell (contained in the embryo 
sac of the ovule) by a sperm cell of the pollen tube. 




Young pine trees near the parent tree. Photograph from U. S. Department of 

Agriculture. 

Seed Dispersal.^ — If you will go out any fall afternoon into 
the fields, a city park, or even a vacant lot, you can hardly 

^At this point a field trip may well be taken with a view to finding out how 
the common fall weeds scatter their seeds. Fruits and seeds obtained upon this 
trip will make a basis for laboratory work on the adaptations of seed and fruit for 
dispersal. 

HUNT. NEW ES. — 4 



42 



FRUITS AND THEIR USES 



escape seeing how seeds are scattered by the parent plants and 
trees. Several hundred little seedling trees may be counted often 
under the shade of a single maple or oak tree. But nearly all 
these young trees are doomed to die, because of the overshading 
and crowding. Plants, like animals, are dependent upon their 
surroundings for food and air. They need light even more than 
animals need it, because the soil directly under the shade of the 
old tree gives only raw food material to the plants, and they 
must have sunlight in order to make food. This overcrowding is 
seen in the garden where young beets or lettuce plants are grow- 
ing. The gardener assists nature by thinning out the young plants 
so that they may not be handicapped in their battle for life in the 
garden by an insufficient supply of air, light, and food. 

It is evidently of considerable advantage to a plant to be able 
to place its progeny at a considerable distance from itself, in 
order that the young plants may be provided with sufficient 
space to get nourishment and foothold. This is the result 
which plants have to accomplish. Some accomplish the result 

more completely than others, 
and thus are the more suc- 
cessful ones in the battle of 
Hfe. 

Adaptations for Seed Dis- 
persal;- Fleshy Fruits with 
Hard Seeds. — Plants are 
fitted to scatter their seeds 
by having the special means 
either in the fruit or in the 
seed. Various agents, as the 
wind, water, or squirrels, 
birds, and other animals, 
make it possible for the seeds to be taken away from the 
plant. 

Fleshy fruits, that is, such fruits as contain considerable water 
when ripe, are eaten by animals and the seeds passed off un- 
digested. Most wild fleshy fruits have small, hard, indigestible 
seeds. Birds are responsible for much seed planting of berries 
and other small fruit. Bears and other berry-eatmg animals aid 




The blackberry, a fruit having small seeds 
scattered by birds. 



SEED DISPERSAL 



43 




in this as well. Some seeds have especial adaptations in the 
way of spines or projections. Insects make use of these projec- 
tions in order to carry them away. Ants plant seeds which 
they have carried to their nests for a food supply. Nuts are 
planted by squirrels and blue jays. 

Suggestions for Field Work. — Examine the fruit of huckleberry, black- 
berry, wild strawberry, wild cherry, black haw, wild grape, tomato, currant. 
Report how many of the above have seeds with hard coatings. Notice 
that in most, if not in all, edible fruits, the fruit remains green, sour, and 
inedible until the seeds are ripe. In the state of nature, how might this 
be of use to a plant? 

Hooks and Spines. — Some fruits which are dry and have a 

hard external covering when ripe possess hooks or spines which 

enable the whole fruit to be carried away from 

the parent plant by animals or other moving 

objects. Cattle are responsible for the spread 

of some of our worst weeds in this way. The 

burdock and clotbur are familiar examples. 

In both the mass of little hooks is all that 

remains of an involucre. Thus the whole fruit 

cluster may be carried about and seeds scat- 
tered. In many of the Composites, as 
in the cockleburs and beggar's-ticks, the 
fruits are provided with strong curved 
projections which bear many smaller 
hooklike barbs. 

Pappus. — Probably the most impor- 
tant adaptations for dispersal of seeds 
are those by which the fruit is fitted for 
dispersal by the wind. That much- 
loved and much-hated weed, the dande- 
lion, is an example of a plant in which 
the whole fruit is carried by the wind. 
The parachute, or pappus, is an out- 
growth of the ovary wall. Many other 
fruits, notably that of the Canada thistle, 

are provided with the pappus as a means of getting away. In 

the milkweed the seeds have developed a silky outgrowth which 



Cocklebur. Notice 
the curved hooks. 




Dispersal of dandelion 
fruits. 



44 



FRUITS AND THEIR USES 



may carry them for miles. In New York city the air some- 
times contains the down from these seeds, brought from far 
over the meadows of New Jersey by the prevaihng westerly 
wind. 

Dehiscent Fruits and how they Scatter Seeds. — One of the 
many methods of scattering seeds is seen in dry fruits. These 
simply split to allow the escape of the seeds. Examples of 
common fruits that split open, called dehiscent (de-his'ent) fruits, 
are seen in the fol'lide of the milkweed, a fruit which splits along 
the edge of one valve, the pod or leg'ume of the pea and the bean, 




Dehiscent fruits: A, green pea pod, with valves twisting and expelling the seeds; 
B, milkweed follicle; C, Jimson vv^eed capsule. 



and the capsule of Jimson weed and the evening primrose. The 
wild geranium, a five-loculed capsule, splits along the edge of 
each locule, snaps back, and throws the seed for some distance. 
Jewelweed and witch-hazel fruits burst open in a somewhat 
similar manner. 

Winged Seeds. — The seeds of the pine, held underneath the 
scales of the cone, are prolonged into wings, which aid in their 
dispersal. The seeds of many of our trees are thus scattered. 
Can you name five trees that have winged seeds? 

Other Methods. — Sometimes whole plants are carried by 
the high winds of the fall. The tumbleweed, as it dries, assumes 



SEED DISPERSAL 



45 




a somewhat spherical shape; the main stalk breaks off, and the 
plant may then be blown along the ground, scattering seeds as 
it goes, until it is ultimately stopped by a fence or bush. A 
single plant of Russian 
thistle may thus scatter 
over two hundred thou- 
sand seeds. 

Seeds or fruits (for 
example, the coconut) 
may fall into the water 
and be carried thou- 
sands of miles to their 
new resting place, the 
fibrous husk providing a 
boat in which the seed 
is carried. 

Other seeds collect 
the mud along the 



in 

banks of ponds and 
streams. Birds which 
come there to feed 
carry away many seeds 
in the mud attached to 
their feet. The great English naturalist, Charles Darwin, raised 
eighty-two plants from seeds thus carried by a bird. It is prob- 
able that most of the vegeta- 
tion on the newly formed 
coral islands of the Pacific 
Ocean has come from seeds 
brought to them by birds and 
by water. 

Indehiscent Fruits. — Dry 
fruits which do not split open to allow of the escape of their 
seeds are known as in' dehiscent fruits. Such are nuts, one-seeded 
fruits with usually hard outer covering, the so-called key fruits of 
the maple or ash, and many others. Corn, wheat, oats, etc., are 
indehiscent fruits. A grain is simply a one-seeded fruit in which 
the wall of the ovary has grown so close to that of the seed that 



Various methods of seed dispersal: A, 
clematis fruit; B, clot bur; C, beggar's-tick; D, 
squirting cucumber ejecting seeds after absorb- 
ing water until the pressure is sufficient to push 
out the stopperlike stem; E, wild geranium 
discharging seeds. 




The acorn, a nut in which the involucre 
partly covers the fruit. 



46 



FRUITS AND THEIR USES 




they cannot be separated. Some indehiscent fruits are light and 
carried by the wind; others may be scattered by animals. 

Large Numbers of Seeds. — Plants which do not have especial 
means for scattering their seeds may make up for this by pro- 
ducing a large number of seeds. The Jimson 
weed is a familiar example of such a plant. 
Each capsule of Jimson weed contains from 
four hundred to six hundred seeds, depend- 
ing upon its size. If ail of these seeds de- 
veloped, the whole earth would soon be cov- 
ered with Jimson weed, to the exclusion of 
aU other forms of plant life. That this is 
not the case is due to the fact that only 
those seeds which are advantageously placed 
can develop; the others will, for various 
reasons (lack of moisture to start the young 
seed on its way, poor soil, lack of air or sun- 
light, overcrowding), fail to germinate. 

The Struggle for Existence. — Those 
plants which provide best for their young 
are usually the most successful in 
life's race. Plants which combine 
with the ability to scatter many 
seeds over a wide territory the ad- 
ditional characteristics of rapid 
growth, resistance to dangers of ex- 
treme cold or heat and to attacks of 
parasitic enemies, inedibility, and 
peculiar adaptations to cross-pollination or self-pollination, are 
usually called weeds. They flomish in the sterile soil of the 
roadside and in the fertile soil of the garden. By means of rapid 
growth they kill other plants of slower growth by usurping their 
territory. Slow-growing plants are thus actually exterminated. 
Many of our common weeds have been introduced from other 
countries and have, through their numerous adaptations, driven 
out other plants which stood in their way. Such is the Rus- 
sian thistle. First introduced from Russia in 1873, it spread so 
rapidly that in twenty years it bad appeared as a common 



Grain; spikes of rip- 
ened flowers. 




Key fruit of maple. 



ECONOMIC VALUE OF FRUITS 47 

weed over an area of some twenty-fiye thousand square miles. 
It is now one of the greatest pests in our Northwest. 

Problem. To learn something about the economic value of some 
fruits. {Laboratory Manual, Prob. IX; Laboratory Problems, 
Prob. 85.) 

Economic Value of Grains. — Our grains are the cultivated 
progeny of wild grasses. Domestication of plants and animals 
marks epochs in the advance of civilization. The man of the 
stone age hunted wild beasts for food, and lived like one of them 
in a cave or wherever he happened to be; he was a nomad, a 
wanderer, with no fixed home. He may have discovered that 
wild roots or grains were good to eat; perhaps he stored some 
away for future use. Then came the idea of growing things at 
home instead of digging or gathering the wild fruits from the 
forest and plain. The tribes which first cultivated the soil made 
a great step in advance, for they had as a result a fixed place 
for habitation. The cultivation of grains or cereals gave them 
a store of food which could be used at times when other food was 
scarce. The word '^ cereal " (derived from Ceres, the Roman 
goddess of agriculture) suggests the importance of this crop to 
Roman civilization. From earliest times the growing of grain 
and the progress of civilization have gone hand in hand. As 
nations have advanced in power, their dependence upon the 
cereal crops has been greater and greater. 

'* Indian corn," says John Fiske, in The Discovery of America, 
" has played a most important part in the discovery of the New 
World. It could be planted without clearing or plowing the 
soil. There was no need of threshing or winnowing. Sown in 
tilled land, it yields more than twice as much food per acre as 
any other kind of grain. This was of incalculable advantage to 
the English settlers in New England, who would have found it 
much harder to gain a secure foothold upon the soil if they had 
had to begin by preparing it for wheat or rye." 

To-day, in spite of the great wealth which comes from our 
mineral resources, live stock, and manufactured products, the 
surest index of our country's prosperity is the size of the wheat 
and corn crop. 



48 



FRUITS AND THEIR USES 



Corn. — More than three bilhon bushels of corn were raised 
in the United States in the year 1920. This figure is so enor- 
mous that it has but httle meaning to us. In the past half 
century our corn crop has increased over 350 per cent. Illinois 
and Iowa are the greatest corn-producing states in this coun- 
try, each having a yearly record of over four hundred million 
bushels. 

Indian corn is put to many uses. It is a valuable food. It 
has a large proportion of starch, from w^hich glucose and al- 




Corn-producing regions in the United States. 

cohol are made. It contains some oil, which is used for food, 
as a lubricant, and for making soap. The leaves and stalk are 
an excellent fodder; they can be made into paper and packing 
material. Mattresses can be stuffed with the husks. The pith 
is used as a protective belt placed below the water line of 
our huge battleships. Corncobs are used for fuel, one hundred 
bushels having the fuel value of a ton of coal. 

Wheat. — Wheat is the crop of next greatest importance in 
this country. Nearly eight hundred millions of bushels were 
raised here in 1920, representing a value of nearly $1,000,- 
000,000. Seventy-two per cent of all the wheat raised comeg 



ECONOMIC VALUE OF FRUITS 



49 



from the North Central States and California. Much of the 
wheat crop is exported, nearly half of the exports going to 
Great Britain. Wheat is used chiefly after being manufactured 
into flour. The germ, or young wheat plant, is sifted out 
during this process and made into breakfast foods. Flour- 




Wheat-producing regions. 



making forms the chief industry of Minneapolis, Minnesota, 
and of several other large and wealthy cities in this country. 

Other Grains. — Of the other grains or cereals raised in this 
country, oats are the most important crop, over one and one 
half billion bushels having been produced in 1920. Illinois, Wis- 
consin, Minnesota, and Iowa together produce over 50 per cent 
of the total yield. Oats are distinctly a northern crop, over 
95 per cent being grown north of the parallel of 36°. Barley is 
a staple of some of the northern countries of Europe and Asia. 
Although a hardy cereal, almost three fourths of the total pro- 
duction in the United States comes from California, Minnesota, 
Wisconsin, Iowa; the production of these states may be roughly 
estimated as 200,000,000 bushels. 

Rye is the most important cereal crop of northern Europe, 



50 



FRUITS AND THEIR USES 



Russia, Germany, and Poland producing over 50 per cent of the 
world's supply. It makes the principal food for probably one 
third the people of Europe, being made into '' black bread." 
It is of relatively less importance as a crop now in the United 
States than in former years, only 70,000,000 bushels being pro- 
duced in 1920. 

Perhaps one of the most important grain crops for the world, 
although relatively unimportant in the United States, is rice. 
Its fruit, after threshing, screening, and milling, forms the prin- 
cipal food of one third of the human race. Moreover, its stems 
furnish straw, its husks make a bran used as food for cattle, 
and the grain, when distilled, is rich in alcohol. 

Nearly related to the grains are grasses. The United 
States has a forage crop (exclusive of corn stalks) of over 100,- 
000,000 tons, valued at nearly $1,000,000,000. The best hay in 
the eastern part of the country comes from dried timothy grass 
and clover, the stems and leaves as well as the fruits forming 
the so-called hay. In some parts of the West a kind of clover 
called alfalfa is much grown, as it is adapted to the semi-arid 
conditions of that part of the country. 




Cotton-producing regions. 



ECONOMIC VALUE OF FRUITS 



51 



Cotton. — Among our fruits cotton is probably that of the 
most importance to the outside world. The United States pro- 
duces over thi'ee fourths of the world's cotton supply, and a 
large proportion of the crop is exported. Nearly 12,000,000 
bales were raised in 1920. 

The cotton plant is essentially a warmth-loving plant. Its 
commercial importance is gained because the seeds of the fruit 
have long filaments attached to them. Bunches of these fila- 
ments, after treatment, are easily twisted into threads from 
which are manufactured cotton cloth, muslin, calico, and cam- 
bric. In addition to the fiber, 
cottonseed oil, a substitute 
for olive oil, is made from the 
seeds, and the refuse makes an 
excellent fodder for cattle. 

Cotton Boll Weevil. — The 
cotton crop of the United 
States has been threatened 
rather recently with destruc- 
tion by a beetle called the 
cotton boll weevil. This in- 
sect, introduced from Mexico 
in 1894, has now spread over 
almost the entire cotton- 
raising area of the South. It 
bores into the young pod of 
the cotton and develops there, 
stunting the growth of the 
fruit to such an extent that seeds may not be produced. The 
loss in Texas alone has been estimated at over $10,000,000 a 
year. This weevil, because of the protection offered by the 
cotton boll, is very difficult to exterminate. The weevils are 
destroyed by birds, the infected bolls and stalks are burned, 
millions are killed each winter by cold, they are the prey of 
other insects; but at the present time they are one of the 
greatest pests the South knows. The best method of fighting 
them seems to be planting the cotton early so that it will ripen 
before the boll weevil matures. 




Chamber for fumigating imported 
bales of cotton at Boston, Massachu- 
setts, to guard against the entry of the 
pink boll worm, another great pest. 



52 



FRUITS AND THEIR USES 



Garden Fruits. — Green fruits and vegetables have come to 
play an important part in the dietary of man. People in this 
country are beginning to find that more vegetables and less meat 
are better than the meat diet so often used. 

Some of the niost important fleshy fruits — squashes, cucum- 
bers, pumpkins, and melons — are examples of the pepo (pe'po) 
type of fruit; tomatoes and peppers are tj^pes of berries in 
botanical language, for a berry is any soft or juicy fruit con- 




Various tj^pes of fruits: A, berry (pepper); B, pepo (cucumber); C, drupe 
or stone fruit (cherry); D, pome (pear); E, aggregate fruit made up of drupelets 
(raspberry). 

taining small seeds. The so-called berries — strawberries, rasp- 
berries, and blackberries — of our gardens bring in an annual in- 
come of $25,000,000 to our fruit raisers. Beans and peas are 
important as foods because of their relatively large amount of 
protein. Canning green corn, peas, beans, and tomatoes has 
become an important business. 

Orchard and Other Fruits. — In the United States over 
175,000,000 bushels of apples are grown every year. Pears, 
plums, apricots, peaches, and nectarines also are raised in large 
orchards, especially in California. Nuts form one of our im- 
portant articles of food, largely because of the great amount of 
protein contained in them. 

The grape crop of the world is commercially valuable, because 
of the raisins and wine produced. Lemons, oranges, and grape- 



ECONOMIC VALUE OF FRUITS 53 

truit are of commercial value ' in this country as well as in other 
parts of the world. Figs, ohves, and dates are staple foods in 
the Mediterranean countries and are sources of wealth to the 
people there, as are coconuts, bananas, and many other fruits 
in tropical countries. 

Beverages and Condiments. — The coffee and cocoa *^ beans," 
both products of tropical regions, form the basis of two very im- 
portant beverages of civilized man. Coffee is a stimulant, while 
cocoa and chocolate rank high in food value. Black and red 
pepper, mustard, allspice, nutmegs, cloves, and vanilla are all 
products of various fruits or seeds of tropical plants. 

Summary. — This chapter has shown us that fruits hold seeds, 
that the destiny of the plant depends largely upon the adapta- 
tions which the plant has for scattering its seeds. Hence we 
find varied devices in fruits and seeds for getting the seeds placed 
as far as possible from the parent plant. 

To man seeds and fruits have a commercial and economic 
value. Man's life on the earth may be said to depend largely 
upon his control over the cereal crops. 

Problem Questions. — 1. What are the parts of a typical fruit? 

2. Classify the adaptations in fruits for scattering seeds. 

3. Classify devices in seeds for scattering. 

4. Name five pairs of seeds and fruits which have the same 
method of dispersal. 

5. Explain why three different weeds are so plentiful. 

6. Make a classification of fruits, giving characteristics of 
each group. 

7. Discuss the economic importance of five different crops in 
the United States. 

Problem and Project References 

Beal, Seed Dispersal. Ginn and Company. 

Brigham and McFarlane, Essentials of Geography. American Book Company. 

Dana, Plants and their Children, pages 27-49. American Book Company. 

Duncan, Home Vegetables and Home Fruits. Charles Scribner's Sons. 

Fisher, Resources and Industries of the United States. Ginn and Company. 

Hodge, Nature Study and Life, Chapters X, XI. Ginn and Company. 

Hunter, Laboratory Problems in Civic Biology. American Book Company^ 

Moore and Halligan, Plant Production, Chapter XII. American Book Company. 

Sharpe, A Laboratory Manual. American Book Company. 

U. S. Dept. of Agriculture, Farmers Bulletins 78, 154, 218, 225, 255, 334, 408, 818. 



VI. SEEDS AND SEEDLINGS 



Problem. A study of seeds in their relation to the new plant. 
{Laboratory Manual, Prob. X; Laboratory Problems, Probs. 
42 to 50.) 

(a) The relation of the young plant to its food supply. 

(6) How the young plant makes use of its food supply. 

Relation of Flower to Fruit. — We have already found in our 
study of the fruit that the bean pod is a direct outgrowth from 
the flower. It is, in fact, the ovary of the flower, with the part 
immediately surrounding it, which has grown larger to make a 
fruit. 

Use of Fruit. — The fruit holds and protects the seeds until 
the time comes when they are able to germinate and produce 

new plants like the original plant 
from which they grew. Then, as 
we have seen, it may help to scat- 
ter them far and wide. 

The Bean Seed. — We have 
already been able to identify in 
the pod of the bean the style, 
stigma, and ovary of the flower. 
The opened pod discloses the 
seeds lying along one edge of the 
pod, each attached by a little 
stalk to the inner wall of the 
ovary. If we pull a single bean 
from its attachment, we find 
that the stalk leaves a scar on the coat of the bean; this scar 
is called the hilum (hi'lum). The tiny hole near the hilum is 
the micropyle. Turn back to the Figure (p. 26) showing the fertiU- 
zation of an ovule. Find there the little hole through which the 
pollen tube reached the embryo sac. This hole or micropyle 
remains and is found in the seed. The thick outer coat, or 

54 




spyle- 



Vil 



ura 



plixmul 



Wpocoty! 



B 



A bean seed: A, entire; B, after 
removing the testa or outer coat 
and one cotyledon. 




FOOD IN THE BEAN SEED 55 

testa, is easily removed from a soaked bean; the delicate inner 
coat may escape notice. The part of the bean remaining seems 
to consist of two parts, which are called the colyledoiis (kot-i- 
le'dunz); but if you separate them very carefully, you find the) 
following structures between them. The rodlike part is called 
hypocotyl (hi-po-kot'il, meaning under the cotyledons). This will 
later form the root and part of the stem of the young bean 
plant. The first true leaves, very tiny structures, are folded 
together between the cotyledons and are known as the plu'mule 
or epicofyl (meaning above the cotyledons). The parts of the 
seed within the seed coats all together form the embryo or young 
plant. A bean seed contains, then, a tiny plant tucked away 
between the cotyledons and protected by a tough coat. 

Food in the Cotyledons. — The problem now before us is to 
find out how the embryo of the bean is adapted to grow into 
an adult plant. Up to this stage of its existence it has had the 
advantage of food and protection from the parent plant. Now 
it must begin the battle of life alone. We shall find in all our 
work with plants and animals that the problem of food supply 
is always the most important problem to be solved by the grow- 
ing organism. Let us see if this embryo is able to get a start 
in life (similar to that which many animals get in the egg) from 
food provided for it within its own body. 

Starch in the Bean. — If we mash up a little piece of a bean 
cotyledon which has been previously soaked in water, and test 
for starch with iodine solution, the character- 
istic blue-black color appears, showing the 
presence of starch (p. 14). If a httle of the 
stained material is mounted in water on a 
glass slide under the compound microscope, 
we find that the starch is contained in little 
ovoid bodies called starch grains. The starch 
grains and other food products are made use cells ^S a^T^an:^ cw, 

of by the growing plant. cell wall; sg, starch 

Starches and sugars make up the great ^^^^"' 
class of nutrients known as carbohydrates. Of these we shall 
learn more when we take up the study of foods. (The teacher 
may here refer to the chapter on Foods.) 




56 



SEEDS AND SEEDLINGS 



Protein in the Bean. — Another nutrient present in the bean 
cotyledon is 'protein, as may be proved by a test with nitric acid 
and ammonium hydrate as directed on page 15. 

The cotyledon contains not less than 23 
per cent of protein, 57 per cent of carbohy- 
drates, and about 2 per cent of fats. 

Beans and Peas as Food for Man. — The 
young plant within a pea or bean seed is 
well supplied with nourishment which it 
uses during its germinating, or until it is 
able to take care of itself. In this respect 
it is somewhat like a young animal within 
the egg, a bird or fish, for example. So 
much food is stored in leg'umes (as beans 
and peas are named) that man has come to 
consider them a very valuable and cheap 
source of food. 

Corn. — The ear of corn is not a single 
fruit, but a large number of fruits in a 
cluster, like a bunch of bananas, for ex- 
ample. The husk of an ear of corn is sim- 
ply a covering of leaflike parts which has 
grown over the young fruits for their better 
protection. The corncob is the much thick- 
ened flower stalk on which the flowers were 
clustered. The so-called silk of corn is 
nothing more than a long style and stigma. 
The corn grain itself was also part of the 
flower — the same part that formed the pod 
of the bean with its contained seeds. The 
corn grain is a complete fruit and not 
merely a seed. 

Structure of a Grain of Corn. — Exami- 
nation of a well-soaked grain of corn discloses a difference in 
the two flat sides of the grain. A light-colored area found on 
one surface marks the position of the embryo; the rest of the 
grain contains the food supply. The scar marking the former 
attachment of the silk is found near the outer edge of the grain. 




Longitudinal section 
of young ear of corn: O, 
the fruits; *S, the stig- 
mas; SH, sheathlike 
leaves; ST, the flower 
stalk or peduncle. 
(After Sargent.) 



FOOD SUPPLY OF CORN 



57 



A grain cut lengthwise perpendicular to the flat side and then 
dipped in weak iodine shows two distinct parts, an area con- 
taining considerable starch, the en'dosperm, and the embryo or 
young plant. Careful inspection shows the hypocotyl and plu- 
mule appearing as two points (the latter pointing up toward the 
free end of the grain) and a part surrounding them, the single 
cotyledon (see Figure). Here again we have an example of a 
fitting for future needs, for in this fruit the one seed has 
at hand all the food material necessary for rapid growth, 
although the food is stored outside the embryo. 

Endosperm the Food Supply of Corn. — We do not find that 
the one cotyledon of the corn grain serves the same pxKpose 
to the young plant as do the two 
cotyledons of the bean. Although 
we find a little starch in the corn 
cotyledon, still it is evident from 
our tests that the endosperm is the 
chief source of food supply. The 
study of a thin section of the corn 
grain under the compound micro- 
scope shows us that the starch 
grains in the outer part of the en- 
dosperm are large and regular in 
size, while those near the edge of 
the cotyledon are much smaller and irregular, having large holes 
in them. We know that the germinating grain has a much 
sweeter taste than that which is not growing. This is noticed 
in sprouting barley or malt. We shall find later that, in order 
to make use of starchy food, a plant or animal must in some 
manner change it over into sugar. This change is necessary 
because starch cannot be absorbed by the young plant, while 
sugar can be. 

Starch changed to Grape Sugar in the Corn. — That starch 
is changed to grape sugar in the germinating corn grain can 
easily be shown in the following way. Cut lengthwise through 
the embryos of half a dozen grains of corn, place them in a test 
tube with some Fehling's solution, and heat to the boiling point. 
As no reaction occurs, no grape sugar is present in ungerminated 

HxTNT. New Es. — 6 




Grain of com, in section and 
side view: E, endosperm; C, 
cotyledon; P, plumule; H, hy- 
pocotyl. 



58 



SEEDS AND SEEDLINGS 



corn. Treat in the same way a half dozen grains of corn which 
have germinated, and they will give a brick red color showing 
the presence of sugar along the edge of the cotyledon and between 
it and the endosperm. 

Digestion. — This change of starch to grape sugar in the corn 
is a process of digestion. Test a bit of unsweetened cracker 
(which we know contains starch) with Fehling's solution to 
show that no grape sugar is present. Chew some of the cracker 
a short time and notice that it will begin to taste sweet. Test 
the chewed cracker with Fehling's solution, and grape sugar will 
be found. Here again a process of digestion has taken place. 
Both in the corn and in the mouth, the change from starch to grape 
sugar is brought about by the action of peculiar substances known 

as digestive ferments, or enzymes 
(en'zimz), and the result is that sub- 
stances which before digestion would 
not dissolve in water are now soluble. 
The Action of Diastase on Starch. 
— The enzyme found in the coty- 
ledon of the corn, which changes 
starch to grape sugar, is called 
di'astase. It may be separated from 
the cotyledon and used in the form 
of a powder. 

To a little starch in half a cup of 
water we add a very little (1 gram) 
diastase and put the vessel contain- 
ing the mixture in a warm place, 
where the temperature will remain 
nearly constant at about 98° Fahren- 
heit. On testing part of the con- 
tents at the end of half an hour, 
we find that some of the starch has 
been changed to grape sugar. The 
next morning we find that the starch 
has been almost completely changed. Starch and warm water, 
under similar conditions will not react to the test for grape 
sugar. 




The use of the endosperm to 
corn: A, seedlino; with endo- 
sperm removed ; B, normal seed- 
ling; C, seedling with starch st 
in place of endosperm. 



COTYLEDONS 



59 



Suggested Experiment. — Germinating corn grains, if deprived of their 
endosperm, soon die. But if the endosperm is removed and a Uttle corn- 
starch paste is stuck to the embryo in place of the endosperm, the develop- 
ment will be but little affected (see Figure, p. 58). Evidently the enzyme 
formed in the cotyledon has the power to digest the starch paste, and the 
cotyledon transfers the digested food to the growing parts of the embryo. 





A hardwood forest showing representative 
dicotyledonous trees. 



A pine seedling. 
Note the number of 
cotyledons. 



Other Foods in Corn Grain. — Other foods are present in the 
corn grain. A test for protein shows a considerable amount 
of this food. Oil also is found, and a small amount of mineral 
matter. 

Monocotyledons, Dicotyledons, and Polycotyledons. — Plants 
that bear seeds having but a single cotyledon are called mono- 
cotyle'dons. Although we find many monocotyledonous plants in 
this part of the world, the group is characteristic of the tropics. 
Sugar cane and many of the large trees, such as the date palm, 
palmetto, and banana, are examples. Among the common mono- 



60 SEEDS AND SEEDLINGS 

cotyledons of the north temperate zone are corn, lily, grass, and 
asparagus. 

DicotyWdons, or plants having two cotyledons in the seed, are 
those with which we come in contact most frequently in daily 
Hfe. Many of our garden vegetables, peas, beans, squashes, melons, 
etc., all of our great hardwood forest trees, beech, oak, birch, 
chestnut, and hickory, used for the ^Hrim" of houses, all of our 
fruit trees, pears, apples, peaches, and plums, and, in fact, a very 
large proportion of all plants Uving in the north temperate zone, 
are dicotyledons. 

A third type of plant, with several cotyledons, is the group 
called the poly cotyle' dons, represented by the pines and their 
kin. Such plants furnish most of the lumber and shingles used 
in the construction of frame houses. The soft woods (as the 
pines, hemlocks, spruces, and other '' evergreens ") are also of 
much value in the manufacture of paper. The wood-pulp in- 
dustry has grown to such proportions as to be a menace to our 
softwood forests. 

Problem. A study of the factors necessary for awakening 
{germinating) the embryo within the seed. {Laboratory Manual^ 
Prob. XI; Laboratory Problems, Probs. 33 to 37,) 

(a) The part played by moisture, 

(6) The function of temperature, 

(c) The use of oxygen, 

(d) The use of food. 

In making a series of experiments it is important to keep the 
conditions uniform, varying only the one we are testing. 

External Factors which determine the Growth of Seeds. — 
We know that a dry seed, after lying dormant and apparently 
dead for months and sometimes for years, will, when the proper 
stimuli are apphed to it, wake up and show signs of Hfe. Some- 
thing from outside the seed must evidently start the growth of 
the little embryo within the seed coats. There are several 
factors which are absolutely necessary for germination, as this 
beginning of growth is called. 

Water a Factor. — We can prove that the bean seed will 
take up a considerable amount of water and that it swells 
during the process. Fill a flowerpot almost to the top with dry 



GERMINATION 



61 



beans, cover them securely as shown in the following illustration, 
and place the flowerpot in water overnight. The force exerted 
by the swelling seeds is sufficient to break the flowerpot. A 
dry seed will not germinate. 
The exact amount of water 
which is most favorable for 
the germination of a seed can 
be determined only by careful 
experiment. An oversupply 
of water will prevent growth 
of seeds almost as effectually 
as no water at aU. In gen- 
eral the amount most favor- 
able for germination is a 
moderate supply. 

Moderate Temperature is 
Best. — Another factor influ- 
encing the germination of seeds is that of temperature. The 
temperature at which different varieties of seeds germinate varies 
greatly. As a general rule, increase in temperature is favorable 




The expansive force of germinating 
seeds. The flowerpot to the left was 
filled with dry beans, a block of wood 
wired on, and the whole apparatus placed 
in a pail of water overnight. The result 
is shown at the right. 




Effect of water upon the growth of trees. The trees were all planted at the same 
time in soil that is sandy and uniform. They are irrigated by a small stream rim- 
ning from left to right. Most of the water soaks in before reaching the last trees. 



62 



SEEDS AND SEEDLINGS 



up to a certain point, beyond which it is injurious to the young 

plant, and seeds exposed to a moderate temperature do better 

in the long run than those in the heat. 

Light has a certain marked effect on young seedlings, which 

will be considered when we take up the growth of the stem in 

more detail. 

Some Part of the Air a Factor. — It is an easy matter to 

prove that peas or beans will not germinate without a supply 

of air. Equal numbers of 
soaked peas, placed in two 
flasks, one tightly stoppered, 
the other having no stopper, 
with identical conditions of 
hght, temperature, and mois- 
ture, show that the seeds in 
both flasks start to germinate, 
but that those in the closed 
flask soon^stop growing while 
the others continue to grow 
almost as well as similar seeds 

Experiment to show that some part of placed in an Open dish. 

^^T'^^'^T^^fZ^. Why did not the seeds in 

A test of the air in B shows an excess of the closed flask germinate? 
carbon dioxide; how do you account for ^^ ^^^^ ^^^^ ^^^^ ^^ ^.^j^^g^ 
this? 

the energy contained in a piece 
of coal it must be burned or oxidized. This requires a constant 
supply of fresh air containing oxygen. The seed, in order to 
release from its food supply the energy necessary for growth, 
requires oxygen, so that the oxidation of food may take place. 
Hence a constant supply of fresh air is an important factor in ger- 
mination. It is necessary that air should penetrate between the 
grains of soil around a seed. 

Food oxidized in the Germinating Seed. — But can it be 
proved that food substances are burned up during the germi- 
nation of the seeds? The hmewater test shows the presence of 
carbon dioxide in the closed flask. The carbon in the foodstuffs 
of the pea united with the oxygen of the air, forming carbon 
dioxide. Growth stopped as soon as the oxygen was exhausted. 




GERMINATION 



63 



The presence of carbon dioxide in the flask is an indication that 
a very important process which we associate with animals rather 
than plants, that of respiration, is taking plaee. 

Internal Factors Necessary for Germination. — We have seen 
that stored food is found in the seed and is used by the embryo 
in getting a start in Hfe. But to grow it is also necessary that 
the embryo be aUve and that aU parts be present. We speak of 
the vitahty of a seed, meaning its abihty to germinate. No mat- 
ter how favorable the external conditions may be, no growth will 
take place unless the embryo is ahve. 

Problem. What becomes of the parts of the embryo during growth 
into a young plant ? (Laboratory Manual, Prob. XII ; Laboratory 
Problems, Prob. 25.) 

Germination. — If you plant a number of soaked kidney beans 
in damp soil or sawdust and at the end of each day remove 




A series of early stages in the germination of a kidney bean. A, 
hypocotyl just appearing; B, hypocotyl curving downward; C, 
hypocotyl arched, pulling out the cotyledons; D, hypocotyl lifting 
cotyledons up, first true leaves appearing; E, cotyledons being used 
up, first true leaves expanded, h, hypocotyl; c, cotyledon; p, 
plumule. 

one, you will be able to obtain a complete record of the 
growth of the kidney bean. The first signs of germination are 
the breaking of the testa and the pushing outward of the 



64 



SEEDS AND SEEDLINGS 




hypocotyl to form the first root. A little later the hypocotyl "be- 
gins to curve downward. An older stage shows the hypocotyl 
forming an arch and dragging the bulky cotyledons upward. The 
hypocotyl, as soon as it is released from the ground, straightens 

out, and the cotyledons are 
raised and opened. From 
between the cotyledons the 
budhke plumule or epicotyl 
grows upward, forming the 
true leaves and all of the 
stem above the cotyledons. 
As growth continues, we no- 
tice that the cotyledons be- 
F come smaller and smaller, 
imtil eventually, their food 
contents having been ab- 
sorbed into the young plant, 
they dry up and fall off. 
The young plant is now able 

Experiment to show the function of the to Care for itself. All the 

cotyledonsofthepea:a,plantwithbothcoty- gf^^g^g passed throuoh bv the 
ledons, b, with one removed, c, with both re- . , . 

moved. A at end of one week; Bat end of yOUng plant, from the time the 

three weeks. ^^^^ begins to sprout Until u 

can take care of itself by m^ans of its roots and leaveSj are known 
OS the stages of germination. 

In the pea, hkewise, growth is at first made largely at the 
expense of the cotyledons, which never rise above ground. 
Removal of the cotyledons from a few germinating peas, and 
exposure of these peas to the same conditions as an equal num- 
ber that are normal, show that the loss of the cotyledons retards 
growth and may result in the death of the seedlings. 

Seeds with Endosperm. — In the seeds of the pea and bean 
we have found that the embryo takes up all the space within 
the seed coats. There are some dicotyledonous plants that have 
food stored outside of the embryo. Such a plant is the castor 
bean. A section cut vertically through the castor bean discloses 
a white oily mass directly under the seed coats. This mass is 
called the endosperm. If it is tested with iodine, it will be found 



USES OF SEEDS TO THE PLANT 



65 



to contain starch; oil is also present in considerable quantity. 
Within the endosperm lies the embryo, a thin, whitish structm*e. 
The Uses of Seeds to the Plant. — Not only does a seed serve 
to continue a species of plant in a certain locality, but it serves 
to give the plant a foothold in new places. Moving to a new 
home may be accompHshed, as we shall see later, to a limited 
degree by cuttings, grafting, and in other ways, but the usual 
way is by the production and dispersal of seeds. Seeds blown 
by the wind, carried by animals, or distributed by a hundred 




AiTangement of embryo in its relation to fhe endosperm: 
A, asparagus; B, pine; C, castor bean; D, morning glory; E, 
peanut, c, cotyledons ; e, endosperm; A, hypocotyl; p, plumule; 
t, testa. 

devices, work their way to pastures new, there to establish 
outposts of their kind. 

Inunense numbers of seeds are produced by a single plant. 
This is of great economic unportance. A single pea plant may 
produce twenty pods, each containing from six to eight seeds. 
This would mean the possibiHty of nearly twenty-five thousand 
plants being produced from the original parent by the end of 
the second season and the rapid ^production of a source of food 
for mankind. A plant of Indian corn may yield over fifteen 
hundred grains of corn. On the other hand, many weeds pro- 
duce seed in still greater numbers. A single capsule of Jimson 
weed has been found to hold over six hundred seeds. One milk- 
weed may set free over two thousand seeds. The thistle is even 
more prolific. 

Some seeds, especially those of weeds, are able to withstand 
great extremes of heat and cold and still to retain their ability 



66 



SEEDS AND SEEDLINGS 




Milkweed fruit, showing method of seed 
dispersal. 



to germinate. Some have been known to retain their vitahty 
for over fifty years. In plants, the seeds of which show unusual 

hardiness, it is found 
that the food supply is 
often so placed as to 
protect the delicate 
parts of the embryo 
from injury. The food 
is in a form not easily 
dissolved by water or 
broken up by the action 
of frost, so that it is 
kept in a hard state 
until a time when it is 
softened by the process 
of digestion during the 
growth of the plant. It 
can be seen that plants 
bearing seeds having some of the above characteristics have a 
great advantage over plants bearing seeds that are poorly 
protected. 

Problem. To study some methods of plant breeding. (Labora- 
tory Manual, Prob. XIII; Laboratory Problems, Probs. 155 
to 158.) 

Plant Breeding: Variation of Plants. — Examination of a row 
of plants in a garden, of a hundred dandelion plants, or careful 
measurements made on the pupils in a classroom, would show 
us that no two plants and no two boys or girls have exactly 
the same measurements or characteristics. Each plant and 
animal tends to vary somewhat from its parent. This universal 
tendency among plants and animals is called the law of 
variation. 

But a plant or animal hands down to its offspring the charac- 
teristics which it possesses, usually with only slight variations. 
Each one of us resembles our parents or our grandparents more 
closely than other persons, and far more closely than individuals 
of another race or species. Each plant produced from seed will 



PLANT BREEDING 



67 



be in most respects like the plant which produced the seed. This 
is the law of hered'ity. 

These two laws, of variation and of heredity, the basis on which 
Charles Darwin explained liis theory of evolution, are made use 
of by plant and animal breeders. Since plants tend to vary and 
since such variations may be continued in their offspring, plant 
breeders have helped nature by artificially selecting and prop- 
agating the plants showing the characteristics wanted. In this 
way most of the varieties of our domesticated plants and 
animals have been developed. 

Selective Planting. — By selective "planting we mean choosing 
the best plants and planting the seed from these plants with a view 
to improving the yield. 
In doing this we select 
not necessarily the 
best fruits or grains, 
but the seeds from 
the best plants. A 
wheat plant should be 
selected not from its 
yield alone, but from 
its abihty to stand 
disease and unfavor- 
able conditions. By 
careful seed selection, 
some western farmers have increased their wheat production 
by 25 per cent. This, if kept up all over the United States, 
would mean over $250,000,000 a year in the pockets of the 
farmers. 

Boys and girls who have gardens of their own can easily try 
experiments in selection with almost any garden vegetable. 
Corn is one of the best plants to experiment with. Gather for 
planting only the fullest ears and those with the largest kernels. 
You must also select from the plants those that produce the 
most ears. Plant these carefully selected corn grains in a plot 
by themselves in the garden, and compare their yield with that 
of the nonselected corn. The above picture shows what can be 
done by selection. Plants thus produced may become, by gradual 




a b 

Improvement of corn by selection: a, improved 
type; b, original type from which it was developed. 



68 SEEDS AND SEEDLINGS 

changes through many generations, new varieties of the original 
species from which they sprang. 

Hybridizing and Other Methods. — We have already seen 
that pollen may be carried from one flower to another of the 
same species, and produce seeds. If pollen from one plant be 
placed on the pistil of another of an allied species or variety, 
fer'tihzation may take place and new plants be eventually pro- 
duced from the seeds. Such plants are called hy'brids. 

Hybrids are extremely variable and often are apparently much 
unhke either parent plant. Such are some of the results of 
Luther Burbank's work with the hybrid plums, the Department 
of Agriculture experunents in the crossing of oranges and lemons, 
and the formation of thousands of new varieties of garden plants 
of various kinds — beans, peas, tomatoes, and the hke. By far 
the greatest possibihties for the farmer or fruit grower seem to 
come from hybridizing. 

Another method of obtaining new varieties of plants is that 
discovered by a Dutchman named Hugo de Vries. He found 
that a great variation might arise suddenly (instead of by 
gradual changes), thus producing a new variety which would at 
once breed true. Such a variation is called inutation, and the 
plant showing the new character is called a mutant. This law is 
of great value to breeders, as new plants or animals considerably 
unhke their parents may thus be formed and perpetuated. In 
1862 a Mr. Fultz, of Pennsylvania, found three heads of beard- 
less or bald wheat while passing through a large field of bearded 
wheat. He saved them, sowed them by themselves, and pro- 
duced a quantity of wheat now^ loiown favorably all over the 
world as the Fultz wheat. The seedless orange is another 
example of a mutant. 

Still more important is the discovery made by the monk Gregor 
Mendel. By experimenting with peas he found the laws under 
which certain characteristics are passed on to the descendants. 
Some of these unit characters, such as color of the pea, the shape 
of the pods, and smoothness of coat, always appear in certain 
proportions in the offspring, and some characters tend to dis- 
appear rather than others, when peas having different characters 
are cross bred. These facts have been so carefully worked out 



PLANT BREEDING 69 

that we know just what will happen if we cross breed certain 
plants having definite characteristics. It is to be expected that 
by a more extensive study of ''Mendel's laws" plant breeders 
will be able to produce desired characters and to predict exactly 
what will happen as a result of cross breeding. 

Summary. — We have found that within the seed a baby plant 
or embryo exists. Either packed around the embryo (as endo- 
sperm) or as a part of it (the cotyledons) is the food supply. 
When external conditions of temperature, moisture, and supply 
of oxygen are favorable, the embryo is awakened to activity and 
passes through the stages of germination. 

We have seen also how the two factors of heredity and varia- 
tion have produced new varieties of plants in the hands of 
scientific breeders. 

Problem Questions. — 1. What are the chief differences be- 
tween the bean and corn? Are they both seeds? 

2. What is digestion? How is it brought about? Why is 
it necessary? 

3. How are the forms of plants determined by their seeds? 

4. What are the factors which influence germination? How 
do they do this? 

5. What becomes of each part of a kidney bean after germi- 
nation ? 

6. What are the uses of seeds to a plant? to man? 

7. Discuss three factors in plant breeding. j 

Problem and Project References 

Atkinson, First Studies of Plant Life, Chapters I, II, III, XXV. Ginn and Com- 
pany. 
Bailey, Plant Breeding. The Macmillan Company. 

Dana, Plants and their Children, pages 50-98. American Book Company. 
De CandoUe, Origin of Cultivated Plants. D. Appleton and Company. 
Downing, The Third and Fourth Generation. University of Chicago Press. 
Harwood, New Creations in Plant Life. The Macmillan Company. 
Hunter, Laboratory Problems in Civic Biology. American Book Company. 
Hunter and Whitman, Civic Science in the Community. American Book Company. 
Moore and Halligan, Plant Production. American Book Company. 
Sharpe, A Laboratory Manual. American Book Company. 
Stevens, Plant Anatomy, Chapter XII. P. Blakiston's Sons and Company. 
U. S. Department of Agriculture, Various Year Books if available will give much 
good project material. Look over list of Farmers Bulletins for topics. 



VII. ROOTS AND THEIR WORK 



Problem. A study of roots, to find out — 

(a) Factors influencing direction of growth. 

(b) Their structure. 

(c) How they absorb soil water. 

(Laboratory Manual, Prob. XIV: Laboratory Problems, Probs 
51 to 57.) 

The development of a bean seedling shows us that the root 
invariably grows firstc One of the most important functions of the 

root to a plant is that of a hold- 
fast, an anchor to fasten it in 
the place where it is to develop. 
In this chapter we shall find 
several other uses of the root to 
the plant: the taking in of 
water, with the mineral and 
organic matter dissolved therein, 
the storage of food, climbing, etc. 
But all functions other than the 
one first stated arise after the 
young plant has begun to de- 
velop. 

Root System. — If you dig up 
a young bean seedling and care- 
fully wash the roots, you will see 
that a long root is developed 
as a continuation of the hypocotyl. This root is called the 
primary root. Roots growing from the primary are called sec- 
ondary, and the roots growing from the latter are tertiary roots. 
The smallest branchings are called rootlets. Collectively all the 
roots and rootlets make up a root system. 

Downward Growth of Root. Influence of Gravity. — Many 
of the roots examined take a more or less downward direction. 

70 









^ 








r/ il '^ 











A root system, showing primary 
and secondary roots. 



DIRECTION OF GROWTH 



71 



We are all familiar with the fact that the force called gravity 
influences life upon this earth to a great degree. Does gravity 
act on the growing root? This question may be answered by a 
simple experiment. 

Plant mustard or radish seeds in a pocket garden, ^ stand it with 
the glass face vertical, and allow the seed to germinate until the 
root has grown to a length of about half an inch. Then, keeping 
the glass face vertical, turn the pocket garden so that the roots 
will be horizontal, and allow it to 
remain for one day undisturbed. The 
tips of the roots now will be found to 
have turned in response to the change 
in position, and to point downward. 
This experiment seems to indicate 
that the roots are influenced to grow 
downward by the force called gravity. 

The response of the plant (or any 
living thing) to gravity is called geot- 
ropism (je-ot'ro-pizm). Roots are 
stimulated to grow downward; hence 
they are said to be positively geotropic 
(je-6-tr6p'ik). 

Experiments to determine Influ- 
ence of Moisture on a Growing 
Root. — The roots in the pocket 
garden grow downward when all 
parts of the blotting paper are equally wet. That moisture has 
an influence on the growing root is easily proved. 

Plant bird seed or the seed of mustard or radish in the under- 
side of a^ sponge, which must be kept wet, and may be sus- 
pended by a string under a bell jar in the schoolroom window. 

1 The Pocket Garden. — A very convenient form of pocket germinator may be 
made in a few minutes in the following manner: Obtain two cleaned four by five 
negatives (window glass will do); place one flat on the table and on it place 
half a dozen pieces of colored blotting paper cut to a size a little smaller than 
the glass. Now cut four thin strips of wood so as to fit on the glass just out- 
side of the paper. Next moisten the blotter, place on it some well-soaked radish 
or mustard seeds or grains of barley, and cover it with the other glass. The whole 
box thus made should be bound together with bicycle tape. Seeds will germinat© 
in this box, and with care may live for two weeks or more. 




Radish roots in a pocket gar- 
den that was turned four times 
in the direction of the arrow. 



72 



ROOTS AND THEIR WORK 



Note whether the roots, when they reach the bottom of the 
sponge, continue to grow downward, or if the moisture in the 
sponge is sufficient to counterbalance the force of gravity and 
pull the roots to one side or upward. 

Another experiment is the folloT\dng: Divide the interior of a shallow 
wooden box into two parts by a partition with an opening in it. Fill the 
box with sawdust. Plant peas and beans in the sawdust on one side of the 
partition, and water them very slightly, but keep the other side of the box 
well soaked. After two weeks, take up some of the seedlings and note the 
position of the roots. 

Water a Factor determining the Course taken by Roots. — 

WoieVj as well as the force of gravity, has much to do with the direc- 
tion taken by roots. Water is found 
below the surface of the ground, 
but sometimes at a great depth. 
In order to obtain a supply of 
water, the roots of plants frequently 
spread out very great distances. 
Most trees, and all grasses, have a 
greater area of surface exposed by 
the roots than by the branches. The 
mesquite bush, a low-growing tree 
of the American and Mexican 
deserts, often sends roots down- 
ward for a distance of forty feet 
after water. The roots of alfalfa, a 
clover-hke plant used for hay in the 
western states, frequently penetrate the soil after water for a dis- 
tance of ten to twenty feet below the surface of the ground. 

Structure of a Taproot. — To understand the structure of the 
root, it wiU be easiest for us to examine a large, fleshy one. so 
that we may get a httle first-hand evidence as to its internal 
structure. A taproot is an enlarged primary root which stores 
food — such as a carrot or parsnip. It shows the chief parts in 
its composition clearly. If you cut open such a root and make 
a cross section of it, you find two distinct areas — an outer 
portion, the cortex, and an inner part, the wood. If you cut 
another root in lengthwise section, these structures show still 




Dandelion root. Notice its length. 



STRUCTURE 



73 



Origin of^^ 
iecondBiyflootsltf 




Cortex 

-Epidermis 
-Wood 

,Xonducting 
tubes 



"Epidermis 

-Cortex 
--f¥ood 



mare plainly and an additional fact is seen; namely, that all the 
secondary roots leaving the main or primary root have a core of 
wood which bores its way out 

through the cortex wherever the 'Wlif— Leaves 

rootlets are given off. The tubes 
which conduct the Hquids up in a 
parsnip may be located by cuttmg _ 

off the tip of the root and placing ^^^1^^ 
the cut end in red ink for twenty- 
four hours. Sections of the parsnip 
will show the red ink in the wood 
and that it is most abundant in 
the outer region of the wood just 
within the cortex. 

Fine Structure of a Root. — If 
we could now examine a much 
smaller and more dehcate root in Conducting^ 
thin longitudinal section under the ^^^^^'' 

compound microscope, we should Lengthwise and cross sections of a 

ftnd the entire root to be made up taproot. 

of cells, the walls of which are rather thin.^ Over the lower 

end of the root, where the growing 
tip is located, is found a collection 
of cells, most of which are dead, 
loosely arranged so as to form a root 
cap. This is evidently an adapta- 
tion which protects the young and 
actively growing cells just under 
the root cap, and as it is pointed, it 
assists in burrowing a hole through 
the earth. In the body of the root 
the wood can easily be distinguished 
from the surroimding cortex. The 
cells of the former have somewhat 
thicker walls. A series of tubehke 

structures may be found within the wood. These are made of cells 

^ Cross sections and longitudinal sections of tradescaaatia roots are excellent for 
demonstration of these structures. 
ixuNT. New Es. — 6. 







t-coprEX 



■ ■EPIDERMIS 



•GROWINGPOINT 
l-'ROOTCAP 

Lengthwise section of end of a grow- 
ing root, much enlarged. 



74 



ROOTS AND THEIR WORK 




which have grown together end to end, the long axis of the cells 
running the length of the main root. In their development these 

cells have lost their small ends, and 
now form continuous hollow tubes with 
rather strong walls. Other cells, which 
have developed greatly thickened walls, 
give mechanical support to the tubehke 
cells. Collections of such tubes, some oj 
which conduct fluids wp and others con- 
duct fluids down, and supporting woody 
cells together make up what are known as 
flhrovas' cular bundles. 

Root Hairs. ■ — Careful examination 
of the root of one of the seedlings of 
mustard, radish, or barley grown in 
the pocket garden shows a covering of 
very minute fuzzy structures which are 
at most an eighth or a sixth of an 
inch in length. They vary in length 
according to their position on the 
root, the longest root hairs being found near the point marked 
U. H. in the Figure, where they are most numerous also. These 
structures, called root 
hairs, are outgrowths of 
the outer layer of the 
root (the epider'mis) , and 
are of very great impor- 
tance to the living plant. 
Structure of a Root 
Hair. — A single root hair 
examined under a com- 
pound microscope will be 
found to be a long, 
threadhke structure, al- 
most colorless in appearance. The cell wall, which is very flexible 
and thin, is made up of ceVlulose, a substance somewhat like wood 
in chemical composition, through which fluids may easily pass. 
If we had a very high power of the microscope focused upon 



Young embryo of corn, 
showing root hairs {R. H.) 
and growing stem (P.). 




Diagram of a root hair: CM, cell mem- 
brane; CS, cell sap; CW, cell wall; P, cy- 
toplasm; N, nucleus; S, soil particles. 



HOW THE ROOT ABSORBS WATER 



75 



this cellulose wall, we should be able to find under it another 
structure, far more delicate than the cell wall. This is called 
the cell membrane. CHnging close beneath the cell membrane is 
the cytoplasm of the cell. The remaining space within the root 
hair is more or less filled with a fiuid called cell sap. Forming a 
part of the Hving protoplasm of the root hair, sometimes in the 
hairhke prolongation and sometimes in that part of the cell 
which is in the epidermis of the root, is a nucleus. The cyto- 
plasm, nucleus, and cell membrane are ahve; all the rest of the 
root hair is dead material, formed by the activity of the hving 
substance of the cell. The root hair is part of a living plant cell 
with a wall so dehcate that water and mineral substances from 
the soil can pass through it into the interior of the root. 

How the Root absorbs Water. — The process by which the 
root hair takes up soil water can better be understood if we 
make an artificial root hair large enough to be easily seen. This 
can be done in the following way: Pour some soft celloidin into 
a tube vial; carefully revolve the vial so that an even film of 
celloidin dries on the inside. Remove the film, 
fill with white of egg, and tie over the end of 
a rubber cork, through which a glass tube is 
inserted. When placed in water, the celloidin 
film gives a very accurate picture of the root 
hair at work. After a short time the liquid 
begins to rise in the tube, water having passed 
through the film of celloidin. 

Osmosis. — We have all noticed how a drop 
of red ink will spread through a glass of clear 
water. This is due to the process called diffu^ 
sion. When two fluids of different density 
are separated by a membrane, diffusion will 
take place through it. This kind of diffusion 
is called osmo'sis. By osmosis two gases or 
liquids of different density when separated by a 
membrane tend to pass through the membrane 
and mingle with each other; but the greater flow is always toward 
the fluid of greater density. The method by which the root hairs 
take up soil water is osmosis. 




An artificial root 
hair, showing osmo- 
sis taking place. 



76 ROOTS AXD THEIR WORK 

Passage of Soil Water in the Root. — We have just seen that 
in an exchange of fluids by osmosis the greater flow is toward 
the denser fluid. Thus it is that the root haii'S take in more fluid 
from the soil than they give to it. The cell sap, which partly 
fills the interior of the root hair, is a fluid of greater density 
than the water in the soil outside. When the root hairs become 
filled with water, the density of the cell sap is lessened, and the 
cells of the epidermis are thus in a position to pass along their 
supply of water to the cells next to them and nearer to the cen- 
ter of the root. These cells, in tm'n, become less dense than 
their inside neighbors, and so the transfer of water goes on by 
osmosis from cell to cell until the water at last reaches the inner 
wood. Here it is passed over to the tubes in the woodj" bundles 
and started up the stem. The pressm-e created bj^ this process 
of osmosis is sufficient to send water up the stem to a distance, 
in some plants, of twenty-five to thu't}^ feet. Cases are on record 
of water having been raised in the bii'ch a distance of eighty-five 
feet. 

Physiological Importance of Osmosis. — It is not an exag- 
geration to say that osmosis is a process of ^dtal importance 
not onh^ to a plant, but to an animal as well. Foods are 
digested or changed into a soluble form in an animal so that they 
may pass through the walls of the food tube by osmosis and 
become part of the blood. Without the process of osmosis we 
should be unable to use much of the food we eat. 

Capillarity. — The force known as capillarity (kap-i-lar'i-ti) 
also accounts for the rise of water in plants and helps it to pass 
through soil. If a nmnber of smaU tubes of different bore be 
placed end down in a dish of water the water will be found to 
rise highest in the tube of smallest diameter, and least in the 
largest tube. This is brought about by the adhesion of the mole- 
cules of water to the glass. This force acts in the conducting 
tubes of plants as well as between the soil particles outside, and 
is a verj" probable factor in the transportation of water. 

Problem. A study of some of the relations between roots and 
the soil. {Laboratory Manual, Proh. XV, Laboratory Problems, 
Probs. 58 to 63.) 



SOIL 



77 



(a) Origin of soil. 
(h) Kinds of soil, 

(c) Water-retaining ability of soil, 

(d) Fertility of soils. 

(e) The relation between root hairs and soil, 
(/) Root tubercles and crop rotation. 

Composition of Soil. — If we examine a mass of ordinary loam 
carefully, we find that it is composed of numerous particles of 
varying size and weight. 
Between these particles, 
if the soil is not caked 
and hard packed, we can 
find tiny spaces. In well- 
tilled soil these spaces are 
frequently formed and 
enlarged. They allow air 
and water to penetrate 
the soil. If we examine 
soil under the micro- 
scope, we find consider- 
able water cHnging to 
the soil particles and forming a delicate film around each parti- 
cle. In this manner most of the water is held in the soil. 

Scientists who have made the composition of the earth a 
study, tell us that once upon a time at least a part of the earth 
was molten. Later, it cooled into soHd rock. Soil making 
began when the ice and frost, alternating with heat, chipped 
off pieces of rock. These pieces in time became broken into 
fragments by action of ice, glaciers, running water, and the 
atmosphere. This process is called weathering. The action of 
the air is largely a process of oxidation. A glance at almost any 
crumbhng stones will convince you of this, because of the yellow 
oxide of iron (rust) disclosed. By slow weathering the earth 
became covered with a coating of inorganic soil. Later, genera- 
tion after generation of tiny plants and animals which Hved in 
the soil died, and their remains formed the first organic mate- 
rials of the soil. As time went on, living things of larger si^e 
paid their contribution to the organic soil. 




Inorganic soil is being formed by weathering. 



78 



ROOTS AND THEIR WORK 



You are all familiar with the difference between the so-called 
rich soil and poor soil. The dark or rich soil simply contains 
more material from dead plants and animals, and forms the 
portion called humus. 

Humus contains Organic Matter; Suggestions for Experiments. — It 

is an easy matter to prove that black soil contains organic matter, for if 
equal weights of carefully dried humus and of soil from a sandy road are 

heated red-hot for some 
time and then reweighed, 
the humus will be found 
to have lost considerably 
in weight, and the sandy 
soil to have lost very 
Uttle. The material left 
after heating is inorganic, 
the organic matter hav- 
ing been burned out and 
most of the products of 
combustion having been 
dissipated in the air. 

Organic soil holds 
water much more readily 
than inorganic soil, as a 
glance at the Figure on 
page 79 shows. If we 
fin the vessels with equal 
weights (say 100 grams 
each) of gravel, sand, 
barren soil, rich loam, 
and leaf mold, and 25 
grams of dry, pulverized 
leaves, then pour equal 
amounts of water (100 
CO.) on each and measure all that runs through, the water that has been 
retained will represent the water supply that plants could draw on from 
such soils. 

The Root Hairs take more than Water out of the Soil. — If 

a root containing a fringe of root hairs is washed carefully, it 
will be found to have httle particles of soil still clinging to it. 
Examined under the microscope, these particles of soil seem to 
be cemented to the sticky surface of the root hair. The soil 
contains, besides a number of chemical compounds of various 




This picture shows how the forests help to cover 
the inorganic soil with an organic coating. 



SOIL 



79 




mineral substances, — lime, potash, iron, silica, and many 
others, — a considerable amount of organic material. Acids of 
various kinds are present in the soil, — such as nitric acid, which 
comes from the dead bodies of plants and animals as they decay 
and oxidize, — and carbonic acid, formed by the union of the 
carbon dioxide from the roots and the water in the soil. These 
acids so act upon certain of the mineral substances that they 
become dissolved in the water which is afterward absorbed by 
the root hairs. 

The proportion of each of these mineral materials is very 
small compared with the water in which they are found. A very 
great amount of water 
must be taken up by the 
roots in order that the 
plant may get the needed 
amount of mineral mat- 
ter with which to build 
its protoplasm. 

Plants will not grow 
well without certain of 
these mineral substances. 
This can be proved by 
the growth of seedlings in 
a so-called nutrient solution. Such a solution contains all the 
mineral matter that a plant uses for food; but if certain ingre- 
dients are left out the plants placed in the solution will not 
live. 

Relation of Bacteria to Free Nitrogen. — Plants and animals 
need the element nitrogen in order to make protoplasm within 
their own bodies. It has been known since the time of the 
Romans that the growth of clover, peas, beans, and other 
legumes in soil causes the ground to become more favorable for 
the growth of other plants. The reason for this has been dis- 
covered in late years. On the roots of the plants mentioned are 
found Httle swellings or nodules; and in each noduje exist 
millions of tiny organisms called bacteria, which take out nitrogen 
from the atmosphere and fix it so that it can be used by the 
plant; that is, they form nitrates (soluble compounds containing 



Experiment to illustrate the kind of soil 
which best retains water: A, gravel; B, sand; 
C, barren soil; D, rich soil; E, leaf mold; 
F, dry leaves. 



80 



ROOTS AND THEIR WORK 



nitrogen) which are useful to plants. Only these bacteria, of all 
living things, have the power to take the free nitrogen from the 
air and make it over into a form that can be absorbed by the 
roots. As all the compounds of nitrogen are 
used over and over again, first by plants, 
then as food for animals, eventually return- 
ing to the soil again, it is evident that any 
7iew supply of usable nitrogen must come by 
means of these nitrogen-fixing bacteria. 

Rotation of Crops. — The facts mentioned 
above are made use of by intelligent farmers 
who wish to make as much as possible from a 
given area of ground in a given time. Such 
plants as are hosts for the nitrogen-fixing 
bacteria are planted early in the season. 
Later these plants are plowed in and a 
second crop is planted. The latter grows 
quickly and luxm'iantly because of the 
nitrates left in the soil by the bacteria which 
lived with the first crop. For this reason, 
clover is often grown on land in which it is 
proposed to plant corn later, the nitrates left 
in the soil thus giving nourishment to the 
Tubercles on the roots ^^^^ plants. This alternation is known 

of soy bean. ^ <=> i. 

as rotation of crops. The annual yield of 
the average farm may be greatly increased by this means. 

Soil Exhaustion may be Prevented. — Besides the rotation of 
crops, other methods are used by the farmer to prevent the 
exhaustion of raw food material from the soil. One method 
known as fallowing is to ailow the soil to remain idle until bac- 
teria and oxidation have renewed the chemical materials used 
by the plants. This is an expensive method, if land is dear. 
The more common method of enriching soil is b}'' means of 
fertilizers, or material rich in plant food. Manure is most fre- 
quently used, but many artificial fertilizers, most of which con- 
tain nitrogen, are used, because they can be more easily trans- 
ported and sold. Such are ground bone, guano (bird manure), 
nitrate of potash, and many others. Most fertilizers contain, 




USES OF ROOTS 



81 



in addition to nitrogen, other important raw food materials for 
plants, especially potash and phosphoric acid. 

Roots help the Plant to Breathe. — Although we shall find 
that leaves are the chief breathing organs of a plant, yet roots 
absorb much oxygen from the soil or the water into which they 
reach. The rows of dead trees around a pond that has been 




Various forms of roots: ^, taproot (dandelion); B, fleshy root 
(beet); C, fibrous root (crowfoot); D, fascicled root (dahlia); 
E, adventitious roots (English ivy, on a wall). 

raised by damming indicates that one cause of the death of 
these trees was lack of oxygen. They were actually drowned. 

The so-called " cypress knees," projections of the roots from 
cypress trees, are adaptations to obtain oxygen. 

Food Storage in Roots and its Economic Importance. — The 
use the plant makes of the food stored in the root may be 
understood if we take up the hfe history of the parsnip. Such 
a plant is called a hien'nial because it produces no seed until 
the second year of its existence, after which it dies. Its growth 
the first summer forms the root we use as food. The food 



82 ROOTS AND THEIR WORK 

stored in its root enables it to get an early start in the spring, 
so as to be better able to produce seeds when the time comes. 
Such plants live only under rather cool climatic conditions. 
Examples of other roots which store food are carrot, radish, 
3^am, and sweet potato. This food storage in roots is of much 
practical value to mankind. ]\Iany of our most common garden 
vegetables, as those mentioned above and the beet, turnip, 
oyster plant, and others, are of value because of the food stored 
in roots. The sugar beet has, in Europe especially, become the 
basis of a great industry", producing in normal times over 40 % 
of the world's sugar suppl3\ The products from other roots are 
used for medicine, as, for example, licorice, rhubarb, mandrake, 
ginger, and asafet'ida. 

Modified Roots. — Although roots are primarily anchoring and 
absorbing organs they may, as we have seen, be used for food 
storage as well. Usualty roots grow as a continuation of the 
hypocotyl of the seedling, but they may appear in unusual 
places on the stem or even from the leaves. Such roots are 
called adventitious. The clinging roots developed from the stem 
of English ivy, the stem roots of quick grass and the prop roots 
of Indian corn are examples. 

Other unusual tj'pes of roots are the air roots of the tropical 
forests. Here plants called epiphytes or air plants live on tree 
trunks and obtain moisture from the nearl}^ saturated air. Still 
other plants, like the mistletoe, actually strike their roots into 
the tissues of other plants and take their nourislmaent from 
them. Such plants are called parasites because they take 
their nourishment directly from other living organisms. 

Summary. — We have found from a study of this chapter 
that roots are very sensitive to the force of gravity and that 
they have become modified for many purposes, as climbing, 
props, or food storage. The principal uses of the root to the 
plant are: 

(1) They serve to hold the plant firmly in the ground. 

(2) They serve to store food. 

(3) They absorb mineral matter and water and transmit them 
to the rest of the plant. 

(4) They help as breathing organs. 



USES OF ROOTS 83 

Problem Questions. — 1. What is geotropism? How does it 
act on roots? 

2. What other factors influence the growth of roots? 

3. What are root hairs and what is their function? 

4. Explain osmosis. 

5. How are roots able to take out mineral matter from the 
soil? 

6. What are nitrogen-fixing bacteria? How do they do their 
work? 

7. What proof have we that roots breathe? 

8. Name some forms of modified roots and show their uses 
to the plant. 

Problem and Project References 

Andrews. Botany All the Year Round, Chapter II. American Book Company. 

Atkinson, First Studies in Plant Life, Chapters IX, XI, XII, Ginn and Com- 
pany. 

Coulter, Barnes, and Cowles, Textbook of Botany, Vol. I. pp. 302-322. American 
Book Company. 

Goff and Mayne, First Principles of Agriculture. American Book Company. 

Goodale, Physiological Botany. American Book Company. 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Ilunter and Whitman, Civic Science in the Home. American Book Company. 

Moore, The Physiology of Man and Other Animals. Henry Holt and Company 

Sharpe, A Laboratory Manual. American Book Company. 

itevena. P^nnt Anatomy, Chapter VI. P. Blakiston's Sons and Company, 



VIII. THE STRUCTURE AND WORK OF THE STEM 



Problem, To learn some- 
thing of the structure and work 
of stems. {Laboratory Manual, 
Prob. XVII; Laboratory Prob- 
lems, Probs. 75 to 78.) 

(a) External structure of a 
dicotyledonous stem (optional). 

(b) Internal structure of a 
dicotyledonous stem. 

(c) Circulation in stems. 

(d) Condition of food passing 
through the stem. 

A bud is said to be '' the 
promise of a branch." Any 




A larch, an excurrent tree (at right), and an 
elm, a deliquescent tree (at left). Photo- 
graphed by W. C. Barbour. 



twig in winter shows 
not only the terminal 
bud, from which next 
season's continuation of 
the branch will come, 
but it also shows lateral 
buds placed just above 
the leaf scars which 
mark where last year's 



leaves were attached. The position of the most active buds 
determines the form of the future tree. If the terminal buds 

84 



DICOTYLEDONOUS STEM 



85 



grow more rapidly than those on the sides, we have a straight, 
tall, excurrent tree with one main trmik. Such are Lombardy 
poplars, pines, and cedars. If on the other hand the lateral 
buds grow faster than the terminal, we have a lower, spread- 
ing form of tree, as the ehn or oak. Such a tree is called 
deliquescent (del-i-kwes'ent) in its method of growth. 

The External Structure of a Dicotyledonous Stem. — A horse- 
chestnut twig in its winter condition shows the structure 
and position of the buds very 
plainly. When the twig grew 
last year the scales which cov- 
ered the outside of the terminal 
bud dropped off, and the young 
shoot developed from the opened 
bud. The scales w^hich dropped 
off left marks forming a little 
ring upon the bark of the twig. 
These rings, collect ivel}' named 
the hud scars, enable one to tell 
the age of the branch. 

Just below the lateral buds 
are marks, known as leaf scars, 
that show the points at which 
leaves were attached. A careful 
inspection of the leaf scars 
reveals certain tiny dotlike traces 
arranged more or less in the 
form of a horseshoe. These 
traces mark the continuations of 
the same fibrovascular bundles 
which pass from the root up 
through the stem and out into 
the leaves, where we see them as the veins which act as the 
support of the soft green tissues of the leaf. The most impor- 
tant y^e to the plant of the fibrovascular bundles is the conduction 
of fluids from the roots to the leaves and from the leaves to the 
stem and root. 

Lenticels and their Uses. — The tiny scars, which look like 




Horse-chestnut twig: th, terminal 
bud ; a, lateral bud ; Is, leaf scar ; 
Z, lenticel; /, flower scar; g, bud scar. 
How many years old is this twig? 
How can you tell? 



86 THE STRUCTURE AND WORK OF THE STEM 



ca- 




little cracks in the bark, are very important organs, especially 
during the winter season, for they are the breathing holes of 

the tree. A tree is alive in win- 
ter, although it is much less 
active than in the warm 
weather. But all the year round 
oxygen is taken in and carbon 
dioxide given off through the 
lenticels (len'ti-selz), as the 
breathing holes in the trunk 
and branches of a tree are 
called. 

A Dicotyledonous Stem in 
Cross Section. — If we cut a 

Cross section of a three-year-old box CrOSS SectioU through a yOUng 

elder: ob, outer bark; ib, inner bark; horse-chestnut Stem, we find it 

ca, cambium layer; w, three rings of gj^^^g ^^lYee distinct regions, 

wood; w, medullary ray; p, pith. . . , , 

ihe center is occupied by the 
spongy, soft pith; surrounding this is found the rather tough 
wood, while the outermost area is called cortex or bark. More 
careful study of the bark reveals ihe presence of three layers — 
an outer layer, a middle 
green layer, and an inner 
fibrous layer. This inner 
layer is made up largely 
of tough fiberlike cells 
known as bast fibers. The 
most important parts of 
this inner bark, so far as 
the plant is concerned, are 
sieve tubes, made by join- 
ing, end to end, long cells 
having perforated ends. f^^^^P^ 
Through these tubes, pass- '^^^^^^^K^^MSM 
ing from cell to cell through ''***' 

the sieveUke ends, food Quarter section of oak. Comparing thi. 

with the precedmg picture, point out the 
materials move downward bark, the eambium layer, the rings of 
from the upper part of wood, and the medullary rays. 




DICOTYLEDONOUS STEM 



87 



the plant, where they are manufactured, to the stem and 
roots. 

In the wood will be noticed (see Figures opposite) many lines 
radiating outward from the pith toward the cortex. These are 
the so-called med'ullary rays, thin plates of pith which separate 
the wood into a number of wedge-shaped masses. These masses 
of wood are composed of many elongated cells, which, placed 
end to end, form thousands of little tubes connecting the leaves 
with the roots. In addition to these are many thick-walled 
cells, which give strength to the mass of wood. In sections of 
wood which have taken several years to grow, we find so-called 
annual rings. The distance between one ring and the next (see first 
Figure on page 86) usually represents the amount of growth in one 
year. Growth takes place from an actively dividing layer of 
cells, known as the cam'hium layer ^ which is located between the 
wood and the bark; it forms wood cells from its inner surface 
and bark from its outer surface. Thus new wood is formed as 
a distinct ring around the old wood.- 




Experiment to show that the skin of the potato (a stem; retards evaporation. 



Use of the Outer Bark. — The outer bark of a tree is pro- 
tective. The cells are dead, the heavy woody skeletons serving 
to keep out cold, as well as to prevent the evaporation of 



88 THE STRUCTURE AXD WORK OF THE STE^I 



liquids from within. ]\Iost trees are provided with a layer of 
corky cells. This layer in the cork oak is thick enough to be of 
commercial importance. The function of the cork}^ layer in pre- 
venting evaporation is easity demonstrated by the potato, which 
is a true stem, though found underground. If two potatoes of 
equal weight are balanced on the scales, the skin having been 
peeled from one, the peeled potato will be found to lose weight 
rapidh*. This is due to loss of water, which is held in -by the 
skin of the unpeeled potato. (Figure on page 87.) 

Passage of Fluids up and down the Stem. — If any young 
growing shoot (young seedling of corn or pea, or the older stem 

of gai'den balsam, touch-me-not, or 
sunflower) or an apple twig is placed 
in red ink (eosin), left in the sun 
for a few hom'S, and then examined, 
the red ink will be found to have 
passed up the stem in the woody 
tubes immediately under the inner 
bark. These wood}^ tubes make up 
the inner portion of the fibro-vascu- 
lar bundles called the wood or 
xylem (zl'lem). 

If willow twigs are placed in water, 
roots soon begin to develop from 
that part of the stem which is un- 
der water. If now the stem is 
girdled b}^ removing the bark in a 
ring just above where the roots are 
growing, the part of the stem below 
the girdled area wiU eventually die, 
and new roots will appear above it. The food material neces- 
sary for the outgrowth of roots evident^ comes from above; in 
fact it moves in a downward direction just outside the wood in 
the layer of bark which contains the bast fibers and sieve tubes. 
These sieve tubes make up the outer portion of the fibrovascu- 
lar bundles which is called phloem (flo'em). Food substances are 
also conducted to a much less extent in the wood itself, and 
food passes from the inner bark to the center of the tree by 




Apple twigs split to show 
the course of colored water 
(the dark lines Just inside the 
bark) up the stem. 



CIRCULATION IN STEMS 



89 



way of the pith plates or medullary rays. It is found that 
much starch is stored in this part of the tree trunk. The ex- 
periment with the willow explains why it is that trees die when 
girdled so as to cut the sieve tubes of the inner bark. The food 
supply is cut off from the protoplasm of the cells in the part 
of the tree below the cut area. Many of the canoe birches of 
our Adirondack forest are thus killed, girdled by thoughtless 
visitors. 

In What Form does Food pass through the Stem? — We have 
already seen that materials in solution (those substances which 
will dissolve in water) will pass 
from cell to cell by the process of 
osmosis. This is easily shown 
in the following experiment (see 
Figure). Two thistle tubes are 
partly filled, one with starch and 
water, the other with sugar and 
water, and a piece of parchment 
paper is tied over the lower end 
of each. The lower ends of both 
tubes are placed in a glass dish 
under water. After twenty-four 
hours, the water in the dish is 
tested for starch, and then for 
sugar. We find that only the 

sugar, which has been dissolved by Experiment showing the non-osmo- 
,, . J, 1 ;i sis of starch and water (tube A), and 

the water, can pass through the ^^^^^-^ ^^ ,^g^^ ^^^^^-^^ ^^^be B). 
membrane. 

Digestion. — As we shall see later, the food for a plant is 
manufactured in the leaves or in the stems, etc., wherever green 
coloring matter is found. Much of this food is in the form of 
starch. But starch, being insoluble, cannot be. passed from cell 
to cell in a plant. It must be changed to a soluble form. This 
process of digestion seemingly may take place in all living parts 
of the plant, although most of it is done in the leaves. In the 
bodies of all animals, including man, starchy foods are changed 
in a similar manner, but by different digestive ferments^ into 
a soluble form, grape sugar. 

Hunt. New Es. — 7 




90 THE STRUCTURE AND WORK OF THE STEM 



The food material may be passed in a soluble form until it 
comes to a place where food storage is to take place, then it 
can be transformed to an insoluble form (starch, for example); 
later, when needed by the plant in growth, it may again be 
transformed and sent in a soluble form through the stem to 
the place where it will be used. 

Building of Proteins. — Another very important food sub- 
stance stored in the stem is protein. Of the building of protein, 
little is known. We know it is an extremely complex chemical 
substance which is made in plants from compounds containing 
nitrogen, as the nitrates and compounds of ammonia received 
through the roots from the organic matter contained in the soil, 
and combined with sugar or starches in the body of the plant. 
Some forms of protein substance are soluble and others in- 
soluble in water. White of egg, for example, is very slightly 

soluble, but can be rendered insoluble 
by heating it until it coagulates. In- 
soluble proteins are digested within the 
plant; how and where is but shghtly 
understood. Soluble proteins pass down 
the sieve tubes in the bast and then 
may be stored in the bast, or they may 
pass into the root, fruit, or seeds of a 
plant, and be stored there. 

What forces Water up the Stem. — 
We have seen that the process of osmosis 
is responsible for taking in soil water, 
and that the great extent of the absorb- 
ing surface exposed by the root hairs 
Diagram to show the areas makes possible the absorption of a large 
ma plant through which raw ^mount of Water. Frequently this is 

food materials pass up the 

stem (wavy line in diagram) Hiore than the Weight of the plant every 

and food materials pass dowm twenty -four hourS. 

(even line in diagram). Experiments have been made which 

(After Stevens.) . . 

show that this water is in some way 
forced up the tiny tubes of the stem. During the spring season, in 
young and rapidly growing trees, water has been proved to rise to 
a height of nearly ninety feet. 




MONOCOTYLEDONOUS STEM 



91 



Root pressure is the force with which soil water passes from 
the roots into the stem. This flow of water is the result of 
osmosis in the root hairs and later in the cells of the root. 
But root pressure alone cannot account for the rise of sap 
(water containing materials taken out of the soil) to a height 
of several hundred feet, as in the stems of the big trees of 
California. Other factors that are believed to be at work are the 
cohesion of particles in tiny columns of water, and osmosis between 
living cells that lie along the course of the woody bundles of long 
narrow dead cells that form the 
ducts. But no complete and 
adequate explanation has been n 
found for the rise of sap to great \ 
heights. ' J^ \ 

A very great factor, however, 
is one which will be more fully 
explained when we study the 
work of the leaf. Leaves pass 
off an immense quantity of 
water by evaporation, and this /:. 
process seems to result in a kind 
of suction on the tiny columns of 
water in the stem. In the fall, 
after the leaves have gone, much 
less water is taken in by roots, 

showing that an intimate rela- A broken cornstalk, with cross sec- 
tion exists between the leaves tion (at left) : iV,node; R,r, rind; P, 
J ,1 , p, pith; FV, fv, fibro vascular bundle. 

and the root. 

Structure of a Monocotyledonous Stem. — A piece of corn- 
stalk examined carefully in cross and longitudinal section shows 
us that the main bulk of the stalk is made up of pith, through 
which are scattered numerous stringy, tough structures called 
fibrovascular bundles. The latter are the woody bundles of tubes 
which in this stem pass through the pith and run into the 
leaves, where (in young specimens) they may be followed as 
veins. The outside of the corn stem is formed of large num- 
bers of fibrovascular bundles, which, closely packed together, 
form a hard, tough outer rind. Thus the woody material on 




92 THE STRUCTURE AND WORK OF THE STEM 




the outside gives mechanical support to an otherwise spongy 
stem. 

Structure of a Fibrovascular Bundle in a Monocotyledonous 
Stem. — A cross section of a fibrovascular bundle under the 
microscope shows a collection of supporting cells and ducts 

without any cambium layer. Woody 
cells with thick walls serve to support 
the bundles of tubes. Some, called 
sieve tubes, are developed to carry 
food downward from the leaves, 
while others (see Figure) carry 
water and air upward. The bundles 
elongate rapidly, but are limited 
in their growth outward by the hard- 
walled, woody cells (the xylem). An 
old stem of a monocotyledon con- 
tains more bundles than does a 
Cross section of monocoty- young stem, the bundles growing 

out as veins into the leaves. 

Comparison in the Growth of a 
Dicotyledonous and a Monocoty- 
ledonous Stem. — In the dicoty- 
ledonous stem the woody bundles 
appear in a ring. They are open and grow in both directions, 
inward and outward, from that part of the bundle called the 
cambium. This layer in older stems soon becomes a complete 
ring around the tree. On the outside of the cambium layer is 
found the phloem, or portion containing the sieve tubes which 
bear elaborated food toward the roots. On the inside is found 
the xylem or woody tubes that carry water and air upward. 

In the monocotyledonous stem the bundles are scattered, lack 
the cambium, and increase in number as the stem grows older. 
They contain sieve tubes on the inside and water and air bear- 
ing tubes in their outer part. 

Food Storage. — Many monocotyledonous trees which live for 
long periods of time store food in large quantities in the trunk. 
The sago palm is an example. The sugar cane is a monocot- 
yledonous stem of great commercial value because of the sugar 



ledonous fibrovascular bundle, 
much magnified: ph, sieve tubes 
in which food passes down; d, 
woody portion or bundle ducts 
which carry air and water up- 
ward; p, pith cell. 



BUDDING AND GRAFTING 



93 



contained in its sap. Over 70 pounds of sugar on the average 

is used annually by each person in the United States. Most of 

the cane sugar grown in this country comes from Louisiana and 

Texas, although these 

states do not begin to 

supply the needs of this 

country. 

Various types of stems 
form some of the most 
important sources of 
man's food supply. Our 
common potato, celery, 
onions, rhubarb, aspar- 
agus, and Jerusalem 
artichoke are well-known 
examples. The sago palm 
is the chief support of 
many of the natives of 
Africa. An adult tree 
will furnish 700 pounds 
of sago meal, 2i pounds 
being enough to support 
a man one day. Maple 
sugar is a well-known 
commodity which is ob- 
tained by boiling the sap 
of the sugar maple un- 
til it crystallizes. Over 
16,000 tons of maple 
sugar is obtained every 
spring, Vermont producing about 40 per cent of the total 
output. 

Budding. — We have said a bud is a promise of a branch; it 
may be more, the promise of a new tree. If the owner of an 
apple or peach tree wishes to vary the quality of fruit borne 
by the tree, he may in the early fall cut a T-shaped incision 
in the bark and then insert a bud surrounded with a little bark 
from the tree of the same species bearing the desired fruit. The 




Palm, tapped at the top for its sweet sap, 
from which a drink is made in tropical 

countries. 



94 THE STRUCTURE AND WORK OF THE STEM 

bud is bound in place and left over the winter. When a shoot 
from the embedded bud grows out the following spring, it is 
found to have all the characteristics of the tree from which it 
was taken. This process is known as budding. 








Budding (CBD) and grafting {FG): C, shield-shaped bud from desired variety; 
B, T-shaped incision, ready to receive the bud; D, bud inserted and bound in 
place. F, two grafts from desired variety in place in split end of trunk; G, same 
after application of grafting wax to hold them in place. 

Grafting. — Of much the same nature is grafting. Here, how- 
ever, a small portion of the stem of the closely allied tree is 
fastened into the trunk of the growing tree in such a manner 
that the two cut cambium layers will coincide. This will allow 
the passage of food into the grafted part and insure the ultimate 
growth of the twig. Grafting and budding are of considerable 
economic value to the fruit grower, as they enable him to pro- 
duce at will trees bearing choice varieties of fruit. ^ 

In both of the above processes, the secret of successful growth 
lies in the fact that the cambium surface of the bud or the graft 
comes in contact with the cambium of the tree to which it is 
applied, thus putting it in direct communication with a supply 
of food from the tree which is already established. 

Modified Stems. — We have already seen that the factors of 
the environment, light, heat, gravity, moisture, air currents and 
other factors, act upon the living substance of plants, causing 
them to react in various ways. The changes which take place 
usually fit the plant to succeed better in its battle for life. 

1 For full directions for budding and grafting, see Goff and Mayne, First Prin- 
ciples of Agriculture, Chap. XIX, or Hodge, Nature Study and Life, pages 169-179. 



MODIFIED STEMS 



95 




The potato tuber is a stem; 
note the branches GB growing from 
the "eyes" at one end. Ate is an- 
other "eye." 



Thus various modifications of stems have been brought about. 

Some stems, like the sago palm and potato, become storehouses 

of food. The potato tuber is 

simply a much thickened stor- 
age stem, as one may easily 

prove by examination of the 

so-called '' eyes '' of a sprouting 

potato. The tiny projection 

growing within the eye is a 

bud, which may give rise to a 

branch later. Food and water 

are stored within the tuber. 

Some stems have come to 

exist underground because of 

the protection thus afforded. 

The pest called couch grass or quick grass 
has such a stem. Bulbs, like the onion 
or lily, are examples of stems which have 
become shortened and covered with thick- 
ened leaves, filled with food. Still other stems, 
like that of the dandelion, have become 
reduced in length, which prevents them from 
being broken off by grazing animals. Climb- 
ing stems, as a result of the stimulation of 
the sun, twist around a support in a given 
direction, some revolving with and some 
against the course of the sun. 

We also find stems and leaves modified to 
become holdfasts for the plant. Such are 
the tendrils found in climbing plants. 
Thorns, a protection from animals, may be 
modified parts of leaves or of stems, de- 
pending upon where they come out on the 

Cross and longitudi- stem. (See pictures on the following page.) 

nal section of onion. f, k i. • iiji.j 

Summary. — A stem is a developed bud, 
the form of the plant depending upon the placing of the actively 
growing buds in the young plant. Dicotyledonous and monocot- 
yledonous stems differ in structure, as sunmiarized on page 92. 




96 THE STRUCTURE AND WORK OF THE STEM 



St-eins are seen to act as organs to hold the leaves in a favor- 
able position so as to secure sunlight. They store food for the 
plant and they act as organs to carry soil water and gases from 
the roots to the leaves and to carry elaborated food from the 
leaves to other parts of the plant. 

Problem Questions. — 1. Name all the adaptations found in 
scHKie bud. Give the specific purpose of each adaptation. 





Catbrier; the tendrils T 

are modified stipules (parts 
of leaves); Th, thorn. 



A honey locust; the thorns in this case 
are modified branches (page 95) . 



2. How do Stems help in breathing? 

3. Compare a dicotyledonous and a monocotyledonous stem 
(o) in method of growth; 

(h) in microscopic cross section. 

4. How may insoluble food be made use of by a plant? 
Explain. 



THE STRUCTURE AND WORK OF THE STEM 97 

5. Compare budding and grafting as methods of propagation. 

6. Discuss modifications in stems. 

7. Name ten products obtained from stems. 

Problem and Pboject References 

Andrews, Botany all the Year Round, Chapters VI, VII. American Book Com- 
pany. 

Apgar, Trees of the Northern United States, Chapters II, V, VI. American Book 
Company. 

Atkinson, First Studies of Plant Life, Chapters IV, V, VI, VIII, XXI. Ginn 
and Company. 

Blakeslee and Jarvis, New England Trees in Winter, Bui. 69. Storrs Agricultural 
Experiment Station, Storrs, Conn. 

Dana, Plants and their Children, pp. 99-129. American Book Company. 

Hodge, Nature Study and Life, Chapters IX, X, XI. Ginn and Company, 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

MacDougal, The Nature and Work of Plants. The Macmillan Company. 

Sharpe, A Laboratory Manual. American Book Company. 

Stevens, Plant Anatomy, Chapter X. P. Blakiston's Sons and Companyo 

U. S. Dept. of Agriculture Yearbooks, 1894 to date. 

Ward, The Oak. D. Appleton and Company. 



IX. LEAVES AND THEIR WORK 



Problem, A study of leaves in relation to their environment, 
to show — 

(a) Reactions of stems arid leaves to light. 

(b) Structure. 

(c) Important functions. 

(1) Food-making and its by-product. 

(2) Evaporation of excess water. 

(3) The leaf as a mill (optional). 

(4) Absorption and respiration. 

(d) Means of protection {optional). 

(e) Some leaf modifications {optional). 
(/) Importance to man. 

{Laboratory Manual, Prob. XVIII; Laboratory Problems, 
Probs. 65 to 74.) 

Differences between Roots and Stems. — A comparison of the 
young root and the developing stem of a bean seedKng shows that 

several marked differences 
exist: (1) the color of the 
stem is greenish, while 
the roots are gray or 
whitish; (2) the stem has 
leaves and branches leav- 
ing it in a more or less 
regular manner, while 
the smaller roots are ex- 
tremely irregular in their 
positions on larger roots; 
(3) the stem grows up- 
ward, while the general 
direction taken by the 
roots is downward. 
Effect of Light on Plants. — In young plants which have been 
grown in total darkness, no green color is found in either sterna 

98 




A pocket garden which has been kept in 
complete darkness for several weeks. Notice 
the bleached condition of stems and leaves. 



EFFECT OF LIGHT 



99 



or leaves, the latter often being reduced to mere scales. The 
stems are long and more or less reclining. We can explain this 
strange condition of the seedhng grown in the dark only by 
assuming that light has 
some effect on the pro- 
toplasm of the seedling 
and induces the growth 
of the green part of the 
plant. Numerous in- 
stances could be given 
in which plants grown 
in sunlight are healthier 
and better developed 
than those in the shady 
parts of a garden or 
field. On the other hand, 




The growth of young stems and leaves of oxalis 
toward the light. 



some plants 




Tall straight stems of the hemlock; the trees reach 
up toward the source of light. 



thrive in the shade. 
Such plants are the 
mosses and ferns. 
Still other plants, 
minute organisms, 
some of them invisible 
to the eye, do not 
thrive in the light, 
and may be killed by 
its influence. Exam- 
ples of such are found 
among the molds, 
mildews, and bacteria. 
Such plants, however, 
are not green. As a 
matter of fact, the 
stem of a green plant 
which has but little 
green coloring matter 
develops more rapidly 
under conditions 
where it receives no 
light. 



100 



LEAVES AND THEIR WORK 



Heliotropism. — We saw that the stems of the plants kept in 
the darkness do not always hold themselves erect, as is the case 
of most stems in the light. If seedlings have been growing on a 
window sill, or where the light comes in from one side, you have 
doubtless noticed that the stem and leaves of the seedlings in- 
cline in the direction from which the light comes. The tendency 
of young stems and leaves to grow toward sunlight is called positive 
heliot'ropism. 

The experiment pictured on this page shows this effect of 
light very plainly. A hole was cut in one end of a cigar box and 




Two stages in an experiment to show that green plants grow toward the light. 

barriers were erected in the interior of the box so that the 
seedling growing in the sawdust received its light by an indirect 
course. The young seedling in this case responded to the in- 
fluence of light and grew out finally through the hole in the box 
into the open air. This growth of the stem to the light is of 
very great importance to a growing plant, because, as we shall 
see later, food making depends largely on the amount of sunlight 
the leaves receive. 

Effect of Light. — We have already found that seedlings grown 
in total darkness are almost yellow-white in color, that the 
leaves are but slightly developed, and that the stem has de- 
veloped far more than the leaves. We have also seen that a 



ARRANGEMENT OF LEAVES 



101 



green plant will grow toward the source of light, even against 
great odds. It is a matter of common knowledge that green 
leaves turn toward the light. Place growing pea seedlings, 
oxalis, or any other plants of rapid growth near a window which 
receives full sunlight. Within a short time the leaves are found- 
to be in positions to receive the most sunlight possible. 

Arrangement of Leaves. — A study of trees in a park, or in the 
woods, shows that the trunks of trees which are close together 





A lily, showing long, narrow 
leaves. 



A dandelion, showing a whorled arrange- 
ment of long, irregular leaves. 



are usually tall and straight and that the leaves come out 
in clusters near the top of the tree. The leaves lower down 
are often smaller and less numerous than those near the 
top. Careful observation of plants growing outdoors shows us 
that in almost every case the leaves are so disposed as to get 
the most sunlight. The ivy climbing up the wall, the morning- 
glory, the dandelion, and the burdock all show different arrange- 
ments of leaves, each presenting a large surface to the light. 
Leaves are usually definitely arranged, and fitted in between 
others so as to present their upper surface to the sun. Such 
an arrangement is known as a leaf mosaic. Good examples of 
such mosaics, or leaf patterns, are seen in trees having leaves 
which come up alternately, first on one side of a branch, then 
on the other. Here the leaves turn, by the twisting of their 



102 



LEAVES AND THEIR WORK 



stalks, so that they all present theu* upper surface to the 
sun. In the case of the dandelion, a rosette or whorled cluster 
of leaves is found. In the horse-chestnut, where the leaves come 
out opposite each other, the older leaves have longer stems 
than the young ones. In the mullein the entii'e plant forms a 
cone; the old leaves near the bottom 
have long stalks, and the little ones 
near the apex come out close to the 





Palmately-veined leaf of 
the maple. 



The skeleton of a pinnately 
veined leaf: MR, midrib; P, the 
leafstalk or petiole; V, the veins. 



main stalk. In every case each leaf receives a large amount of 
light. Other modifications of these forms may easily be found 
on a field trip. 

The Sun a Source of Energy. — We all know the sun is a 
source of energy, for do we not feel its heat and is not heat a 
form of energy ? Solar engines have not thus far come into any 
great use, because fuel is cheaper. Actual experiments have 
shown that the sun gives to the earth vast amounts of energ}^ 
When the sun is in the zenith, energj^ equivalent to one hundred 
horse power is received by a plot of land twenty-five by one 
hundred feet, or the size of a city lot. Plants receive and use 
much of this energy by means of their leaves. 



STRUCTURE OF A LEAF 



103 




Pinnately-compound leaf of rose, show- 
ing stipules St. 



The Structure of a Leaf. — Let us now examine with some 
detail the structure of a simple leaf of a dicotyledonous plant. 

A green leaf shows usually (1) a flat, broad blade which may 
take almost any conceivable shape; (2) a stem or petiole (pet'i-ol), 
which spreads out into veins 
in the blade (the veins usually 
present a netted appearance 
in the leaf of a dicotyledon, 
but run more or less parallel 
to one another in the blade 
of a monocotyledonous leaf); 
(3) stipules, a pair of out- 
growths from the petiole at 
its base. In many leaves the 
stipules fall off early. Some 
leaves are compound, that is, 
each of the little leaflike parts 
is in reality a section of the leaf blade which is so deeply indented 
that it is cut away to the midrib or central vein, as in the rose 

leaf. A pair of stipules found at 
the base sho"ws that such a leaf 
is compound. The cut just above 
shows this condition in the. rose 
plant. What other plants commonly 
seen have compound leaves? 

The Cell Structure of a Leaf. — 
The lower surface of most leaves, as 
seen under the microscope, shows 
large numbers of tiny oval openings 
called sto'mata (singular stoma) . Two 
cells, usually kidney-shaped, are 
found, one on each side of the stoma. 
These are the guard cells. By changes 
in the shape of these cells the open- 
ing of the stoma is made larger or smaller. Larger cells (irregular 
in dicotyledons) form the epidermis, or outer covering of the 
leaf. Study of the leaf in cross section shows that the stomata 
open directly into air chambers between the loosely arranged 




Surface view of epidermis of 
lower surface of a leaf highly 
magnified; e, ordinary epidermal 
cell; g, guard cell. — Tschirch. 



104 



LEAVES AND THEIR WORK 



cells composing the lower part of the leaf. The upper surface 
of leaves sometimes contains stomata, but more often is without 
them. The under surface of an oak leaf of ordinary size con- 
tains about 2,000,000. Un- 
der the upper epidermis is 
a layer of green cells closely 
packed together, called col- 
lectively the palisade layer. 
These cells are more or less 
columnar in shape. Under 
them are several rows of 
rather loosely placed cells 
containing the air spaces 
above mentioned. These 
are called collectively the 
spongy parenchyma (pa- 
reng'ki-ma) . If we happen 
to have a section cut through 
a vein, we find it composed 




LOWEIf 
£PW£M/S 



CUADD CELL 



•STOMA 



Section of a leaf highly magnified. The 
cells containing chlorophyll bodies are in the 
palisade layer and the spongy parenchyma. 



of a number of tubes made up of, and strengthened by, thick- 
walled cells, the fihrovascular bundles. The veins are evidently a 
continuation of the tubes of the stem out into the blade of the leaf. 
Starch made by a Green Leaf. — If we examine the palisade 
layer of the leaf, we find cells which are almost cylindrical in 
form. In the protoplasm of these cells are found a number of 
small green-colored bodies, which are known as chloroplasts 
(klo'rS-plasts) or chlorophyl (klo'r6-fil) bodies. If the leaf is 
placed in wood alcohol, we find that the bodies still remain, but 
that the color is extracted, going into the alcohol and giving to 
it a beautiful green color. The chloroplasts are simply part of 
the protoplasm of the cell colored green. If the plant is kept 
in the sun, the chloroplasts retain their green color, but in the 
dark this color is gradually lost. These bodies are of the greatest 
importance directly to plants and indirectly to animals. The 
chloroplasts, by means of the energy received from the sun, manu- 
facture starch out of certain raw materials. These raw materials 
are soil water, which is passed up through the bundles of tubes 
into the veins of the leaf from the roots, and carbon dioxide, 



STARCH MAKING 



105 




which is taken in through the stomata or pores which dot the 

under surface of the leaf. 

Light and Air Necessary for Starch Making. — Pin strips of 

black cloth, such as alpaca, over some of the leaves of a growing 

geranium in such a way that 

only a part of each leaf is in 

the dark; and place the plant 

in a sunny window for two 

or three days. Then remove 

some of the partly covered 

leaves after a day of bright 

sunhght, and after extract- 
ing the chlorophyl with wood 

alcohol (because the chloro- 
phyl covers up the contents 

of the cells) test for starch. 

We find that starch is present 

only in those portions of the 

leaves which were exposed to 

sunlight. From this experi- 
ment we infer that the sun has 

something to do with starch 

making in a leaf. The necessity of air also for starch making 

may easily be proved: on a plant placed 
in the sunlight cover a leaf with vaseKne; 
after several days it will be found to con- 
tain no starch, while leaves unvaselined 
contain starch. 

Air is necessary for the process of starch 
making in a leaf, not only because carbon 
dioxide gas is absorbed (there are from 
three to four parts in ten thousand pres- 
ent in the atmosphere), but also because 
the protoplasm of the leaf is ahve and 
must have oxygen. These gases are 
taken in through the stomata of the leaf 

from the surrounding air. 

Comparison of Starch Making and Milling. — The manufac- 

HuNT. New Es. — 8 



A hydrangea plant, upon the leaves of 
which strips of black cloth {A) have been 
pinned in order to exclude sunlight. 




Starchless area in leaf, 
caused by excluding sun- 
light by means of a strip 
of black cloth. 



106 



LEAVES AND THEIR WORK 



ture of starch by a green leaf is not easily understood. The 
process has been compared to the milling of grain; in which 
case the mill is the green part of the leaf. The sun furnishes 
the motive power, the chloroplasts constitute the machinery, 
and soil water and carbon dioxide are the raw materials taken 

into the mill. The man- 
ufactured product is 
starch, and a certain by- 
product (corresponding to 
the waste in a mill) is 
also given out. This by- 
product is oxygen. To 
understand the process 
more fully, we must re- 
fer to a small portion of 
the leaf. Here we find 
that the green palisade 
cells perform most of the 
work. The carbon diox- 
ide is taken in through 
the stomata and reaches 
the green cells by way of 

Diagram to illustrate the formation of starch. ,■, • , t, , 

the mtercellular spaces 
and by diffusion from cell to cell. Water reaches the green cells 
through the conducting tubes in the veins. It then passes into 
the cells by osmosis, and there becomes part of the cell sap. 
The light of the sun easily penetrates to the cells of the palisade 
layer, giving the energy needed to make the food. This whole 
process is a very delicate one, and takes place only when exter- 
nal conditions are favorable. For example, too much heat or 
too httle heat stops starch making; the presence of stored food 
in the leaf has a similar effect on the process. This building up 
of starch out of carbon dioxide and water and the release of oxygen 
by chloroplasts in the presence of sunlight is called photosynthesis. 
Chemical Action in Starch Making. — In the process of starch 
making, water (H2O) and carbon dioxide (CO2) are combined in 
such a way as to make starch, expressed by the chemical formula 
CeHioOs. It is probable that the first product formed in the 




STARCH MAKING 



107 



leaf is carbonic acid, which assists in making formaldehyde, 
from which sugar and finally starch is formed. AU of these 
changes are brought about by the action of enzymes which are 
present in the cells of the leaf and help make food manufacture 
possible. The starch thus formed is either stored in the leaf or 
changed by digestion to some soluble form Uke grape sugar, 
which can be carried to other parts of the plant, passing from 




soil water 



Diagram (after Stevens) to illustrate the processes of breath- 
ing, food making, and transpiration which may take place in 
the cells of a green leaf in the sunlight. 



cell to cell by osmosis. The oxygen is passed out through the 
stomata of the leaf. 

Protein Making and its Relation to the Making of Living 
Matter. — Protein material is a food which is necessary for the 
growth of protoplasm, and is present in the leaf, the stem, and 
the root. Proteins can apparently be manufactured in any 
plant cell, the presence of light not being a necessary factor. 
The element nitrogen is taken up by the roots as a nitrate 
(nitrogen in combination with lime or potash) in the soil water, 
and in making protein it unites with the carbon, hydrogen, and 
oxygen found in starch and sugar. Proteins are probably not 
made directly into protoplasm in the leaf, but are stored by the 
ceils and used when needed, either to form new cells at a growing 



108 



LEAVES AND THEIR WORK 



point, or to repair waste. While plants and animals obtain their 
food in different ways, they probably make it into living sub- 
stance {assimilate it) in exactly the same manner. 

Foods serve exactly the same purposes in plants and in 
animals; they either build living matter or they are burned 
(oxidized) to furnish energy (work power). If you doubt that 
a plant exerts energy, note how the roots of a tree bore their 




An example of how a tree may exert energy. This rock has been 
split by the growing tree. Photograph from the American Museum of 
Natural History. 

way through the hardest soil, and how stems or roots of trees 
often split open solid rocks, as illustrated in the Figure. 

Rapidity of Starch Making. — Leaves which have been in 
darkness show starch to be present shortly after being exposed 
to light, Squash leaves make three fourths of an ounce of starch 
for each square yard of surface. A corn plant sends 10 to 15 
grams of reserve material into the ears in a single day. This 
fact explains how the rapid growth seen in grain fields or a 
fruit orchard may occur and is of economic importance. Not 
only do plants make their own food but they store it away, and 
it becomes food for animals as well. It is fortunate that the 
food is stored in such a stable form in grain or other fruits 
that it may be sent to all parts of the world without spoiUng. 
Ajiimals, herbivorous and flesh-eating, even man himself, all are 



OXYGEN GIVEN OFF BY GREEN PLANTS 109 



dependent upon the starch-making processes of the green plant 
for the ultimate source of their food. 

Oxygen given off by Green Plants. — It is possible to prove that 
oxygen is given off by green plants in sunlight. The common 
green frog scum seen in shallow ponds is often so full of bubbles 
that it is buoyed up by them at the water's surface. If some 
of this plant or other green water weed 
is placed in a large battery jar or fruit 
jar in a sunny window, bubbles of gas 
will be seen to arise from it, the amount 
increasing as the water is warmed by the 
sun's rays. 

If a glass funnel is placed upside down 
so as to cover the plants, and then a test 
tube full of water inverted over the 
mouth of the funnel, enough gas may be 
collected to test for oxygen.^ 

That oxygen is given off as a by- 
product when starch is made by green 
plants is a fact of far-reaching impor- 
tance. Parks in a city are true '' breath- 
ing spaces." The green covering of the 
earth is giving to animals an element that 
they must have, while the animals in 
their turn are supplying to the plants 
carbon dioxide, a compound used in food 
making. Thus a relation of mutual help- 
fulness exists between plants and animals. 

Evaporation of Excess Water. — In order to secure the neces- 
sary amount of mineral matter for the manufacture of foods, 
an enormous amount of water is taken up by the roots and 
passed to the leaves, where the minerals which were in solution 
in the soil water are deposited and the excess water is evapo- 
rated through the stomata. The process of giving off water in 




Experiment to show that 
oxygen is given off by green 
plants in the sunlight. 



1 Water contains air in solution, including some carbon dioxide, but the amount 
of this gas in a jar of ordinary water may be too small. Immediate success with 
this experiment will be obtained if the water has been previously charged with 
carbon dioxide. 



110 



LEAVES AND THEIR WORK 



the form of vapor is known as transpiration. That moisture is 
passed out through the blade of the leaf is shown by the dia- 
^am below, di'ops of water having gathered on the inside of 

the bell jar. A small grass plant on a 
summer's day evaporates more than its 
own weight in water. This would make 
nearly haK a ton of water distributed to 
the air dm'ing twentj^-four hom's b}- a 
grass plot twenty-five b}^ one hundred 
feet, the size of the average city lot. 



From which. Surface of the Leaf is Water 
Lost? Experiment. — In order to find out 
whether water is passed out from any par- 
ticular part of the leaf or not, we maj"" remove 
two leaves of the same size and weight from 
some large-leaved plant — a mullein was used 
for the illustrations on the opposite page — and 
cover the upper surface of one leaf and the lower 
surface of the other with vaseline. The petioles 
of both should be covered with wax or vaseline, 
and the two leaves exactly balanced on the pans 
of a balance which has pre\'iously been placed 
in a warm and sunny spot. Within an hour the 
leaf u-hich has the upper surface covered with 
vaseline will show a loss of weight. Microscopic 
examination of the epidermis of a mullein leaf 
shows us that the lower surface of the leaf is 
Experiment to show provided with stomata. It is through these 

transpiration. The top of ^ j^ ^j^^. water is passed out from the 

the flower pot is covered ^. r ^-i ^ e 

^■+v uu n^-u -4- tissues of the leaf. 

with rubber. The moisture 

comes from the leaves. Regulation of Transpiration. — The 

stomata of leaves close at night, the guard cells apparently being 
sensitive to Hght, and prevent the transpiration of much water. 
There is little loss of water on humid daj's, because of the large 
amount of water in the atmosphere. VHien the plant has water 
and the atmosphere is dry, the stomata open and give off water 
vapor. But the exact means by which regulation of evaporation 
through the stomata takes place is not well understood. 
The Effect of Transpiration on Water within the Stem. — It 




RESPIRATION 



111 



has already been noted that root pressure alone will not account 
for the rise of water to the tops of very tall trees. Experiments 
indicate that evaporation of water through the stomata exerts a 




Experiment to show through which surface of a leaf water vapor passes off. 

pull upon the tiny column of water held together by cohesion 
within the stem of the tree, thus causing the rise of water to 
the leaves on the upper branches. 

Respiration by Leaves. — All living things require oxygen. It 
is by means of the oxidation of food materials within the plant's 




rmis 



Section through stomata: in A the stoma is open; in B the stoma is closed; 
s, stoma; g, g, guard cells. 

body that the energy used in growth and movement is released. 
A plant takes in oxygen largely through the stomata of the 
leaves, to a less extent through the lenticels in the stem, and 
through the roots. Thus rapidly growing tissues receive the 



112 



LEAVES AND THEIR WORK 



ox3^gen necessary for them to perform their work. The products 
of oxidation in the form of carbon dioxide are also passed off 
through the same organs. It can be shown by experiment 
that a plant uses up oxygen in the darkness; in the light the 
amount of oxygen given off as a by-product in the process of 
starch making is, of coui'se, much greater than the amount used 
by the plant. 

Economic Uses of Leaves. — The practical us3 of green 
plants to man is very great. They give off oxygen in the sun- 
light and use carbon dioxide, which 
is given off by animals in respiration. 
We should remember, as taxpayers, 
that money spent on city parks is 
money weU invested, bringing as it 
does a source of ox^^gen supply where 
it is most needed. 

Another very important use of 
leaves to man is seen in the fact that 
after falhng to the ground, they help 
to form a rich covering of humus, 
which acts as a coat to hold in moist- 
ure. The forests are our greatest 
source of water supply. The cutting 
away of the forest always means a 
depletion of the reserve water stored 
in soil, with consequent floods and 
droughts in alternation. 

Leaves are used directly by man 
for food. Examples are cabbage, 
lettuce, kale, and broccoh. These 
foods, properly combined with fleshy 
foods, are of great importance in 
giving a balance to diet. In a wider sense, all animals depend 
upon leaves fc^r their food supply, either directly or indirectly. 
Foods obtained from roots, stems, seeds, and fruits were manu- 
factured in the leaves and transported within the plant to their 
places of storage. Even meat-eating animals are in the long 
run dependent upon plants, for they feed upon plant eaters. 




A cactus, sho"«nng the leaves 
modified into spines. 



MODIFIED LEAVES 



113 



Modified Leaves. — Leaves, as well as stems, may be modified 
for the protection of the plant. In some cacti, for example, in 
order to prevent too rapid evaporation of water, the leaves have 
been changed into spines. In other plants, as the mullein, 
the leaves are covered with protective hairs. In still others the 
leaves may be reduced or lost entirely, as in the asparagus. We 
have already noted that some leaves have become modified for 
climbing purposes. 

Leaves as Insect Traps. — The most curious adaptations of 
leaves are seen, however, in those plants whose leaves have been 




Leaves modified to serve as insect traps: A, pitcher plant; B, sundew; C, 

Venus's flytrap. 

modified to catch and feed upon insects. It sometimes happens 
that the environment of a plant will not supply the nitrogen 
necessary for growth. Certain species of plants, therefore, by 
means of either bladder-like leaves, as in the bladderwort and 
pitcher plant, or actual traps, as are seen in the sundew and 
Venus's flytrap, catch and actually use the bodies of the insects 
as food. The accompanying illustrations show how this is 
done. 

Summary. — This chapter shows us (1) that light plays an 
important part in not only attracting stems and leaves but also 
in helping to make food; (2) that the structure of a leaf fits 
it to be a starch making as well as a breathing organ; it also 



114 LEAVES AND THEIR WORK 

makes protein, gives off oxygen as a by-product of starch 
making, and gives off water by transpiration; (3) that starch 
making requires light, carbon dioxide, water, and chlorophyll in 
addition to the delicate mechanism of the leaf; (4) that various 
modifications of leaves serve for protection, storage of water, 
climbing, and catching of insects for food, the last curious modifi- 
cation being brought about by lack of available nitrogen in the 
environment. 

Problem Questions. — 1. What is heliotropism? Give ex- 
amples. 

2. Prove all energy comes from the sun. 

3. Describe the microscopic structure of a leaf. 

4. Describe the process of photosynthesis. 

5. What other functions has the green leaf of a growing 
plant? 

6. Sum up the economic uses of green plants to the world. 

7. Describe five adaptive modifications of green leaves. 

Peoblem ajo) Project References 

Andrews, Botany All the Year Round, pp. 46-62. American Book Company. 

Coulter, Barnes and Cowles, A Textbook of Botany, Vol. I, Part II, and Vol. Vi. 
American Book Company. 

Dana, Plants and their Children, pp. 135-185. American Book Company. 

Densmore, General Botany, Chapter VI. Ginn and Company. 

Gager, Fundamentals of Botany, Part II. P. Blakiston's Sons and Company. 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Lubbock, Flowers, Fruits and Leaves, last part. The Macmillan Company. 

MacDougal, Practical Textbook of Plant Physiology, Longmans, Green, and Com- 
pany. 

Sharpe, A Laboratory Manual. American Book Company. 

Stevens, Plant Anatom.y, Chapter IX. P. Blakiston's Sons and Company. 

Ward, The Oak, D. Appleton and Company. 



X. OUR FORESTS; THEIR USES AND THE 
NECESSITY FOR THEIR PROTECTION 

Problem. To determine some uses of stems (optional). {Labo- 
ratory Manual, Prob. XIX; Laboratory Problems, Probs. 80-84.) 

(a) Special products from stems. 

(b) Some woods and their value. 

(c) Field work in forestry. 

The Economic Value of Trees. Protection and Regulation 
of Water Supply. — Trees form a protective covering for the 
earth's surface. They pre- 
vent soil from being 
washed away, and they 
hold moisture in the 
ground. Without trees 
many of our rivers might 
go dry in summer, while 
in the rainy season sud- 
den floods would result. 
The devastation of im- 
mense areas in China and 
considerable damage by 
floods in parts of Switzer- 




Working to prevent erosion after the removal 
of the forest in the French Alps. 



land, France, and in Pennsylvania, have resulted where the 
forest covering has been removed. No one who has tramped 
through our Appalachian forests can escape noticing the dif- 
ferences in the condition of streams which flow through areas 
covered with forest and those from around which trees have 
been cut. The latter streams often dry up entirely in hot 
weather, while the forest-shaded stream has a never failing 
supply of crystal water. 

Several cities on the Atlantic coast, such as Savannah, Wil- 
mington, and Philadelphia, owe their importance to their po- 
lls 



116 



OUR FORESTS 




Erosion at SajTe, Pa., by the Chemung River. 
Photographed by W. C. Barbour. 



sition on navigable rivers supplied with water largely by the 
Appalachian forests. Should these forests be destroyed, it is 
not impossible that the frequent freshets which would follow 
would so fill the rivers with silt and debris that the ship 

channels in them, al- 
ready costing the 
government millions 
of dollars a j-ear to 
keep di'edged, would 
become too shallow 
for ships. If this 
should occur, these 
cities would soon lose 
theii' importance. 

The story of how 
this veiy thing hap- 
pened to the old 
Greek city of Posei- 
donia is graphically told in the following lines: 

" It was such a strange, tremendous storj-, that of the Greek Poseidonia, 
later the Roman Psestum. Long ago those adventuring mariners from 
Greece had seized the fertile plain which at that time was covered with 
forests of great oak and watered by two clear and shining rivers. They 
drove the Italian natives back into the distant hills, for the white man's 
burden even then included the taking of all the desuable things that were 
being wasted b}' incompetent natives, and they brought over colonists — 
whom the philosophers and moralists at home maligned, no doubt, in the 
same pleasant fashion of our own day. And the colonists cut down the 
oaks, and plowed the land, and bmlt cities, and made harbors, and finally 
dusted their busj^ hands and busy souls of the grime of labor and wrought 
splendid temples in honor of the benign gods who had given them the 
possessions of the Italians and filled them with power and fatness. 

" Every once in so often the natives looked lustfull}' down from the 
hills upon this fatness, made an armed snatch at it, were driven back with 
bloody contumeh', and the heaping of riches upon riches went on. And 
more and more the oaks were cut down — mark that! for the stories of 
nations are so inextricably bound up with the stories of trees — untU aU 
the plain was cleared and tiUed; and then the foothills were denuded, and 
the wave of destruction crept up the mountain sides, and they, too, were 
left naked to the sim and the rains. 

" At first these rains, sweeping down torrentially, unhindered by the 



ECONOMIC VALUE OF TREES 117 

lost forests, only enriched the plain with the long-hoarded sweetness of 
the trees; but by and by the living rivers grew heavy and thick, vomiting 
mud into the ever shallowing harbors, and the land soured with the un- 
drained stagnant water. Commerce turned more and more to deeper 
ports, and mosquitoes began to breed in the brackish soil that was making 
fast between the city and the sea. 

" Who of all those powerful landowners and rich merchants could ever 
have dreamed that little buzzing insects could sting a great city to death? 
But they did. Fevers grew more and more prevalent. The malaria- 
haunted population went more and more languidly about their business. 
The natives, hardy and vigorous in the hills, were but feebly repulsed. 
Carthage demanded tribute, and Rome took it, and changed the city's 
name from Poseidonia to Psestum. After Rome grew weak, Saracen 
corsairs came in by sea and grasped the slackly defended riches, and the 
little winged poisoners of the night struck again and again, until grass 
grew in the streets, and the wharves crumbled where they stood. Finally, 
the wretched remnant of a great people wandered away into the more 
wholesome hills, the marshes rotted in the heat and grew up in coarse 
reeds where corn and vine had flourished, and the city melted back into 
the wasted earth." — Elizabeth Bisland and Anne Hoyt, Seekers in Sicily. 
John Lane Company. 

Prevention of Erosion by Covering of Organic Soil. — Streams 
unprotected by forests may dig out soil and carry it far from 
its original source. Examples of what streams have done may 
be seen in the deltas formed at the mouths of great rivers. The 
forest prevents this by holding back the water and letting it out 
gradually. This it does by covering the inorganic soil with 
humus or decayed organic material which, like a big sponge over 
the forest floor, holds water through long periods of drought. 
The roots of the trees, too, help hold the soil in place and pre- 
vent erosion. The gradual evaporation of water through the 
stomata of the leaves cools the atmosphere, and this tends to 
precipitate the moisture in the air. Eventually the dead bodies 
of the trees themselves are added to the organic covering, and 
new trees take their place. 

Other Uses of the Forest. — In some localities forests are used 
as windbreaks and to protect mountain towns against ava- 
lanches. In winter they moderate the cold, and in summer re- 
duce the heat and lessen the danger from storms. The nesting 
of birds in woods protects many plants valuable to man which 
otherwise might be destroyed by insects. 



118 



OUR FORESTS 



Forests have great commercial importance as well. Even in 
this day of coal, wood is still by far the most-used fuel. It ia 
useful in building. It outlasts iron under water, in addition 
to being strong and light. It is cheap and, with care of the 
forests, inexhaustible, while our mineral wealth will some day 
be used up. Hard woods are chiefly used in house building and 
furniture manufacture; many soft woods, reduced to pulp, are 
made into paper. Distilled wood gives alcohol. Partially 
burned wood is charcoal. Vinegar and other acids are ob" 




FOREST REGIONS 



The forest regions of the United States. 

tained from trees, as are tar, creosote, resin, turpentine, and 
other useful oils. The making of maple sirup and sugar forms a 
profitable industry in several states. 

The Forest Regions of the United States. — The combined 
area of all the forests in the United States, exclusive of Alaska, 
is about 550,000,000 acres. This seemingly immense area is 
rapidly decreasing in acreage and in quality, thanks to the de- 
mands of an increasing population, a woeful ignorance on the 
part of the owners of the land, and wastefulness on the part of 
cutters and users alike. 

A glance at the map shows the distribution of our principal 



USES OF WOOD 



119 



forests. At the present time they occupy about 35 per cent of 
the total area of the country. But lumbering is still one of our 
greatest industries and so heedless are we for the future that at 
the present time we are cutting our forests three times as fast 
as they are being renewed by natural growth. Moreover the 
waste in production is enormous, it being estimated that over 65 
per cent of a tree is wasted before it is used by man. Washington 




Transporting logs from the forest to the mill, Washington. 

ranks first of all the states in the production of lumber. Here 
the great Douglas fir, one of the '^ evergreens," forms the chief 
source of supply. In the Southern states, especially Louisiana 
and Mississippi, yellow pine and cypress are the trees most 
lumbered. 

Uses of Wood. — In our forests much of the soft wood (the 
cone-bearing trees, spruce, balsam, hemlock, and pine), and pop- 
lars, aspens, basswood, with some other species, are made into 
paper. The daily newspaper and cheap books are responsible 
for inroads on our forests which cannot well be repaired. It is 
not necessary to take the largest trees to make paper pulp; 
hence many young trees of not more than six inches in diameter 
are sacrificed. Of the hundreds of species of trees in our forests. 



120 



OUR FORESTS 



the conifers are probabh' most sought after for lumber. Pine, 
especially, is probably used more extensively than any other 
wood. It is used for all hea^y construction work, frames of 
houses, bridges, masts, spars, and timber of ships, floors, rail- 
way ties, and many other purposes. Cedar is used for shingles, 
cabinetwork, lead pencils, etc.; hemlock and spruce for heavy 
timbers and, as we have seen, for paper pulp. Another use for 
our lumber, especialh' odds and ends of all kinds, is in the pack- 
ing-box industr3\ It is estimated that nearly 50 per cent of all 
the lumber cut finds its way ultimatel}' into the construction 
of boxes. Hemlock bark is used for tanning. 

The hard woods, ash, basswood, beech, birch, cherry, chest- 
nut, ehn, maple, oak, and walnut, are used largely for the 
"trim" of om' houses, for manufactm'e of furniture, wagon or 
car work, and endless other pm'poses. 

Structure of Wood. — Quite a difference in color and struc- 
ture is often seen between the heartwood, composed of the dead 
walls of cells occupying the central part of the tree trunk, and 
the sapwood, the H^-ing part of the stem. In trees which are 
cut down for use as lumber and in the manufacture of various 
kinds of fm'niture, the markings and differences in color are not 
always easy to understand. 

Methods of Cutting Timber. — A glance at the diagram of 

the sections of timber shows us 
that a tree may be cut radially 
through the middle of the trunk 
or tangentially to the middle 
portion. Most lumber is cut 
tangentiaUy. Hence the annual 
rings appear in a more or less 
irregular arrangement, causing 
^. , . ^ . ^ grain in the wood, and the elHp- 

Diagrams of sections of timber: a, . 
cross section; b, radial; c, tangential, tical markings SCCU m many 
(From Pinchot, U. S. Dept. of Agr.) gc^^ool desks. 

Knots. — Knots, as can be seen from the diagram on the 
following page, are branches which at one time started in theu' 
outward gro\^i:h and were for some reason killed. Later, the tree, 
continuing in its outward gro-wth, surrounded them and covered 






DESTRUCTION OF THE FOREST 



121 



them up. A dead limb should be pruned before such growth 
occurs. The markings in bird's-eye maple are caused by 
adventitious buds which have not developed, 
and have been overgrown with the wood 
of the tree. 

Destruction of the Forest. By Waste in 
Cutting. — Man is responsible for the de- 
struction of one of this nation's most valu- 
able assets. This is primarily due to wrong 
and wasteful lumbering. Hundreds of thou- 
sands of dollars' worth of lumber is left to 
rot annually because the lumbermen do not 
cut the trees close enough to the ground, or 
because through careless felling of trees many other smaller 
trees are injured. There is great waste in the mills. In fact, 




Section of tree trunk 
showing knot. 




A forest in the Far West totally destroyed by fire and by wasteful lumbering. 

man wastes lumber in every step from the forest to the making 
of the finished product. 

By Fire. — It is estimated that at the present time five 
sixths of our original timber has been cut or burned. During 



HTJNT. NEW ES. 



122 



OUR FORESTS 



the past five years an area greater than that covered by the 
New England states has been destro^^ed by fire. Indirectly, 
man is responsible for fire, one of the greatest enemies of the 
forest. INIost of the great forest fires of recent years, the losses 
from which total in the hundreds of millions, have been due 
either to railroads or to carelessness in setting fires in the woods. 
It is estimated that in forest lands traversed by railroads from 

25 per cent to 90 per cent of 
the fires are caused by coal- 
burning locomotives. For this 
reason laws have been made 
in New York state requiring 
locomotives passing through 
the Adirondack forest pre- 
serve to burn oil instead of 
coal. This has resulted in a 
considerable reduction in the 
number of fires. In addition 
to the loss in timber, the 
fires often burn out the or- 
ganic matter in the soil (the 
"duff") forming the forest 
floor, thus preventing the 
growth of other trees there 
for many years to come. In 
New York and other states 
fires are prevented by an or- 
ganized corps of fire ward- 
ens, whose duty it is to watch 
the forest and fight forest fires. 
Other Enemies. — Other enemies of the forest are numerous 
fungous plants of which we shall learn more later, insect para- 
sites, which bore into the wood or destroy the leaves, and graz- 
ing animals, particularly sheep. Wind and snow also annually 
kill many trees. 

Forestry. — The American forests have long been our pride. 
In Germany, especially, the importance of the forest has long 
been recognized, and the German forester or caretaker of the 




Woodpeckers and other birds protect 
the forest by eating destructive insects. 
Photograph from American Museum of 
Natural History. 



FORESTRY 



123 






> 






forests is well known. In some parts of central Europe, the 
value of the forests was seen as early as the year 1300 A.D., 
and many towns consequently bought up the surrounding 
forests. The city of Zurich has owned forests in its vicinity for 
at least 600 years. In this country only recently has the im- 
portance of preserving and caring for our forests been noted by 
our government. Now, however, we have a Forest Service in 
the U. S. Department of Agriculture; and this and numerous 
state and university schools of forestry 
are rapidly teaching the people of this 
country the best methods for the pres- 
ervation of our forests. The Federal 
Government has set aside a number of 
tracts of mountain forest in some of the 
Western states, making a total area of 
over 167,000,000 acres. New York has 
established for the same purpose the 
Adirondack Park, with nearly 1,500,000 
acres of timber land; Pennsylvania has 
a park of 700,000 acres, and many other 
states have followed their example. 

Methods for Keeping and Protecting 
the Forests. — Forests should be kept 
thinned. Too many trees are as bad as 
too few. They struggle with one another 
for foothold and light, which only a few 
can enjoy. The cutting of a forest should 
be considered as a harvest. The oldest 
trees are the '^ ripe grain," the younger 
trees being left to grow to maturity. 

Several methods of renewing the forest are in use in this 
country. (1) Trees may be cut down and young ones allowed 
to sprout from the stumps. This is called coppice growth. 
This growth is well seen in parts of New Jersey. (2) Areas or 
strips may be cut out so that seeds from neighboring trees are 
carried there to start new growth. (3) Forests may be artifi- 
cially planted. Two seedlings planted for every tree cut is a 
rule followed in Europe. The greatest dangers are from fire 




We must protect our 
city trees. A tree badly 
wounded by "cribbing" 
of horses. 



124 



OUR FORESTS 



and from careless cutting, and these dangers may be kept ir 
check by the efficient work of our national and state foresters. 

A City's Need of Trees. — All over the United States the 
city governments are beginning to realize what European cities 

have long known, that trees 
are of great value to a city. 
Many cities are spending 
money not only to plant trees, 
but for proper protection to 
those already growing. Thou- 
sands of city trees are annually 
killed by horses which " crib" 
upon them (Figure, p. 123). 
This may be prevented by 
proper protection of the trunk. 
The Forester and his Work. 
— A new and attractive pro- 
fession has opened in recent 
years for young men who are 
fond of the great out-of-doors. 
Forest rangers are state or 
national officials whose duty it 
is to protect the forests. They 
watch for and fight fires, patrol 
sections of forest to prevent 

Forest ranger on steel lookout tower, illegal Cutting, regulate Cattle 

watching for forest fires. This tower grazing in forest reserves, and 

is connected with others by telephone. . i i i 

Photograph from Pennsylvania Depart- m general Watch OVer OUr 

ment of Forestry. great national asset, the forests. 

Foresters are appointed by private interests also to take 
practical charge of the care and growth of the forests. 

Chicago has appointed a city forester, who has given the fol- 
lowing excellent reasons why trees should be planted in the 
city: 

(1) Trees are beautiful in form and color, inspiring a constant appreci- 
ation of nature. 

(2) Trees enhance the beauty of architecture. 

(3) Trees create sentiment, love of country, state, city, and home. 




SUMMARY 125 

(4) Trees have an educational influence upon citizens of all ages, es- 
pecially children. 

(5) Trees encourage outdoor life. 

(6) Trees purify the air. 

(7) Trees cool the air in summer and radiate warmth in winter. 

(8) Trees improve climate and conserve soU and moisture. 

(9) Trees furnish resting places and shelter for birds. 

(10) Trees increase the value of real estate. 

(11) Trees protect the pavement from the heat of the sun. 

(12) Trees counteract adverse conditions of city life. 

Let us all try to make Arbor Day what it should be, a day 
for planting and caring for trees; for thus we may help to pre- 
serve this most important heritage of our nation. 

Summary. — Forests are of much importance because they 
(1) regulate our water supplies, (2) prevent erosion, (3) change 
climate, (4) are of great commercial importance. The enemies 
of the forest are wind and other natural forces, fire, and man's 
carelessness in cutting, and his unwillingness to look forward 
into the future. The cure will come through conservation, tree 
planting, and the work of the foresters. 

Problem Questions. — 1. Describe ten uses of the forest. 

2. How might cities depend upon the forest? 

3. Describe five methods of forest destruction. 

4e How can you help to prevent forest destruction? 

Problem and Project References 

A-pgar, Trees of the Northern United States. American Book Company. 

Fernow, Care of Trees. Henry Holt and Company. 

Green, Principles of American Forestry. Wiley. 

Hodge, Nature Study and Life, pp. 365-391. Ginn and Company. 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Murrill, Shade Trees, Bui. 205, Cornell University Agricultural Experiment 
Station. 

Pinchot, A Primer of Forestry, Division of Forestry, U. S. Department of Agri- 
culture. 

Roth, A First Book of Forestry. Ginn and Company. 

Sharpe, A Laboratory Manual. American Book Company. 

Ward, Timber and Some of its Uses. The Macmillan Company. 




XI. THE VARIOUS FORUMS OF PLANTS AND HOV^ 
THEY REPRODUCE THEIMSELVES 

Problem, How to know some forms of plant life. (Optional.) 
{Laboratory Manical, Prob. XX; Laboratory Problems, Probs. 11 4, 

-^ (a) An alga, (c) A moss. 

(5) A fungus. {d) A fern. 

Adaptation to Environment. — Plants, as well as animals, are 

greatl}' affected b}' what immediately suiToimds them, — their 

enviromnent. We have shown 
in om' experiments that a 
variation in the envii'onnient 
(conditions of temperatm'e, 
moistm'e, light, etc.) is capable 
of changing or modif3^ing 
the struct m-e of plants very 
greatly. The changes which 
a plant or animal has under- 
gone, that fit it for conditions 

in which it lives, are called adaptations to environment. 

The first plants probably lived in the water. ^Most of the plants 

wliich are simplest in struc- 
ture still hve m the water. 

In such plants we can 

distinguish no root, stem, 

or leaf. This simplest fonii 

of plant bod}' is called a 

thallus. It maj' consist of 

a single cell or of man}' 

cells; it maj^ be of various 

shapes; but a thallus never 

has the organs belonging to 

higher plants. 

It seems likely that, as 

more land appeared on the . , , , . ^ , ,. . , , 

A red seaweed, showing a imely divided 

.earths smiace, plants be- thallus body. 

126 



A red seaweed, an example of a thallus 
bodv. 




ALG^ 



127 



came adapted to changed conditions of life on dry land. With 
this change in environment came a need of taking in water, 
of storing it, and of conducting it to various parts of the organ- 
ism. Thus we may imagine how plants came to have roots, 
stems, and leaves, adapted to their environment on dry land. We 
find in nature that those plants and animals which are best adapted 






Rockweed, a brown alga, showing the distribution on rocks below high-water mark. 

or fitted to Kve under certain conditions are the ones which 
survive and drive other competitors out from their immediate 
neighborhood. Nature selected those which were best fitted to 
live on dry land, and they have eventually covered the earth 
with their progeny. Gradually the forms of life grew more and 
more complex until at last very complicated organisms such as 
the flowering plants developed. Between the flowering plant 
and the simplest of all plants are several great plant groups 
which show steps in complexity of structure between the most 
lowly and the most highly specialized plants. The simplest of 
all these forms are the algae (arje). 

Algae. — The algae are a diverse collection of plants, con- 



128 FORMS AND REPRODUCTION OF PLANTS 



taining forms of many ^hapes and sizes. The body of an 
alga is a thallus; it may be platelike, circular, ribbon-formed, 
threadlike, filamentous, or even composed of a single cell. A 
large number of the algae inhabit the water. In color they vary 
from green through the shades of blue-green to yellow, brown, 
and red. The latter colors are best seen in the seaweeds, all 
of which, however, contain chlorophyll. 

Green Algae. — The plants known as the green algoe are of 
great interest to us because of their distribution in fresh water, 

and also because of their 
economic importance as a sup- 
ply of oxygen for fish and other 
animals in the waters of our 
inland lakes and rivers. Our 
attention is called to them in 
an unpleasant way at times, 
when, after multiplying very 
rapidl}^ during the hot summer, 
they die suddenly in the early 
fall and leave their remains in 
our water supply. Much of the 
unpleasant taste and odor of 
drinking water comes from this 
cause. 
The city of New York has recently had an unpleasant 
experience with a tiny alga called synu'ra. This little plant, 
although harmless, gives an oily, disagreeable taste to water. 
One part of the water supply in which synura was present in 
large numbers had to be cut off from the main supply and 
treated before it was fit for use. Such 
experiences are not uncommon and are 
usually prevented by treating with 
copper sulphate in dilution. 

Pleurococcus. — Many other forms _., '^ ^ "^ .1 

'^ , Pleurococcus. A, single cell; 

of algae are common. One of the sim- b, colony of four cells formed 

plest is pleurococcus (pl(X)-r6-k6k'us). f'-om the ondnal cell .4 . 

This little plant consists of a single tiny cell, which by division 
may give rise to two or even more cells which cling together 




Synura. 




PLEUROCOCCUS, DIATOMS, POND SCUM 12P 

[n a mass. The green color on tree trunks, stone houses, etc, 
is often due to millions of these little plants. 

Diatoms. — These plants are found in vast numbers living on 
the mud or stones at the bottom of small streams. The plant 
body is inclosed in a cell wall composed largely of silica. Many 
of the diatoms are free-swinuning. They compose a large per- 
centage of the living organisms found near the ocean's surface. 

Pond Scum (Spirogyra). — This alga is well known to every 
boy or girl who has observed a small pond or sluggish stream. 
It grows as a slimy mass of green threads or filaments. Under 
the low power of the microscope, the body of a thread of pond 




Spirogyra: n, nucleus; s, chloropliyll bands. 

scum is seen to be made up of elongated cylindrical cells, each 
of which contains a spirally wound band of chlorophyll bodies. 
Careful study shows the presence of a nucleus held in the 
body of the cell by strands of protoplasm, the remainder of 
the space within the cell being a large vacuole filled with 
cell sap. 

Pond scum may grow by simple division of the cells in a fila- 
ment. This method of asexual reproduction is the way growth 
takes place in the cells of the root, stem, or leaf of a flowering 
plant, but another method of reproduction is also seen in pond 
scum. The cells of two adjoining filaments may push out tubes 
which meet, thus connecting the cells with each other. Mean- 
time the protoplasm of the cells thus joined condenses into two 
tiny spheres; the bands of chlorophyll are broken down, and 
ultimately the contents of one of the cells passes through the 
connecting tube and mingles with the cell of the neighboring fila- 
ment. The result of this process of fusion is a thick-walled rest- 
ing cell which is called a zygospore (zI'g5-spor). The cell thus 
formed can withstand considerable extremes of heat and cold, 
and may be dried to such an extent that it is found in dust 



130 FORMS AND REPRODUCTION OF PLANTS 



or floating in the air. Under favorable conditions, this spore 
will germinate and produce a long filament by asexual repro- 
duction. 

Conjugation. — The process by which two cells of equal size unite 
to form a single cell is called conjugation. It is believed to be a 
sexual process which corresponds in a way to 
fertilization in the higher plants. 

Fungi. — The simplest plants, of which we 

have just seen examples, are called thallophytes 

(tharS-fits). Of these there are two groups, the 

olgw or plants containing chlorophyll, and the 

fungi (fun'ji), or those which do not contain 

chlorophyll. As a direct result of the lack of 

chlorophyll in the cells, the fungi are unable to 

make their own food. They must obtain food 

from other plants or animals. So7ne take up 

their abode upon living plants or animals, in which 

case they are called parasites', others obtain their 

food from dead organic matter and are called 

sapropJujtes (sap'r6-fits). The above facts make 

Conjugation of the group of the fungi of immense economic 

importance to man. We shall consider several 

of these plants in their dii'ect relation to the 

human race. 

Mosses. — These are mostly shade-loving and m.oisture- 

loving plants. They form velvety carpets in many of our 

forests, but they often show their preference for moist localities 

by covering the wooded shores of lakes and swamps. 

Pigeon-wheat Moss. — One of the mosses frequently seen and 
easily recognized is the so-called pigeon-wheat moss. The re- 
semblance of a large number of these plants to a mimic field 
of grain has given the name pigeon- wheat to this form. 

Forms of Moss Plants. — Thi'ee kinds of moss plants appear 
to be present: leafy plants, others bearing a stalk and capsule, 
and still others which terminate at the end in a little rosette 
of leaves, inclosing what appears to be a tiny flower. 

Leafy Moss Plant. — A leafy moss plant has rhizoids (ri'zoidz) 
or hair-like roots, an upright stem, and green leaves. In the 




Spirogyra; zs, zygo 
spore; /, fusion in 
progress. 



REPRODUCTION OF MOSSES 



131 



plants which have a stalk and capsule, the stalk grows directly 
from the end of the leafy plant. 

Sporophyie. — The capsule is the spore-producing part {spo- 
ran'gium) of the moss plant. The stalk and capsule together 
form the sporophyte (spo'r6-fit) or 
spore-producing generation of the 
moss. 

Gametophyte. — The spore germi- 
nates into a threadlike structure, 
called a protone'ma. The proto- 
nema soon develops rhizoids; tiny 
buds appear which in time form the 
adult moss plants. These plants may 
grow only leaves, or they may de- 
velop into plants that bear at the 
summit a little rosette of leaves 
within which lie a number of tiny 
organs holding sperm cells. Other 
moss plants not so tall as the sperm- 
producing plants bear at the sum- 
mit of the stem a tuft of leaves 
which hide a number of small flask- 
shaped structures, each of which 
contains a single egg cell. These two 
kinds of plants form the sexual gen- 
eration of the moss. This stage of 
the plant is called the gametophyte 
(ga-me't6-fit) because it produces the 
gametes or sexual cells, — eggs and 
sperms. After a sperm cell has been 
transferred (usually by means of a drop of dew) to the egg cell, 
a fusion of the two cells takes place. This is the process of 
fertilization. The fertilization of the egg cell results in the 
growth of that part of the plant which forms and bears the 
asexual spores, the stalk and capsule, or sporophyte. These 
spores give rise in turn to a leafy moss plant which bears or- 
gans producing eggs and sperms. This process of reproduction 
by two alternating stages is known as alternation of generations. 




Two moss plants, showing the 
gametophyte G and the sporo- 
phyte S. 



132 FOR]\IS AND REPRODUCTION OF PLANTS 



The Ferns and their Allies. — This group of plants is of 
much more importance in tropical countries, where many more 
forms are found than here. They are cliiefl}^ interesting to us 
in our elementar}^ study because the}^, like the mosses, show 
alternation of generations in their life history. 

Life History of a Fern. — The common fern of om' woods 
begins life as a spore. This germinates into a tiny heart- 
shaped body called a 
prothaVlus which con- 
tains sex organs hold- 
ing sperm and egg cells. 
These cells after ferti- 
lization produce leafy 
structures (fronds) 
which bear the asexual 
spores. These spores 
when ripe germinate in 
the ground and the life 
cycle begins over again, 
a sexual generation al- 
tei'nating with an asex- 
ual generation. 

It may be said that 
the ferns as a group 
have formed a large 
part of the enormous 
deposits of coal (almost 
pm-e carbon) from which 
we now derive the 




Alternation of generations in the fern: The 
fronds F produce groups of spore cases s called 
sori. Each sorus is sometimes covered by an in- 
dusium i. A sorus is made up of sporangia sp, and 
each sporangium forms spores m. A spore may 
gei-minate under favorable conditions to form a 
tiny prothalkis P. Tliis in turn forms two kinds 
of organs, antheridia An, bearing sperms, and 
archegonia Ar, bearing egg cells e. As a result of 
the union of an egg and a sperm cell E, the adult gj^erev tO run OUr mftnv 
fern plant is formed. . *^ 

engines. 
Sexual Reproduction in Flowering Plants. — Flowering plants 
reproduce their kind by the formation of seeds. As we know, 
the flower produces in the ovary structures which are called 
ovules. In the interior of the ovule is found a clear proto- 
plasmic area which is called the embryo sac._ In this area is a 
cell (the egg cell) which is destined to form the future plant. 
In the pollen grain is found another cell, the sperm. This cell, 



SYSTEMATIC BOTANY 133 

after the germination of the pollen grain on the stigma of the 
flower, passes through the pollen tube, enters the ovule, and 
unites with the egg cell. The fertilized egg grows into the young 
plant within the seed, known as the embryo (see pages 25-27). 
This method of reproduction, called sexual reproduction, is 
found in the spermafophytes, that is, all seed-producing plants. 

Botanists have shown that in the spermatophytes there exists 
an alternation of generations as in the mosses and ferns. The 
pollen grain is believed to be a spore, which develops into the 
male gametophyte (the pollen tube), while the embryo sac is 
another spore, within which is found the female gametophyte 
Most of the life of the flowering plant is thus passed evidently 
in the asexual or sporophyte stage. All plants — and all animals 
as well — form the cells which compose their bodies by either 
sexual or asexual growth, and the stage of asexual growth is 
usually separated from the period of sexual growth. 

Systematic Botany. — The plant world is divided into many 
tribes or groups. Not only are plants placed in large groups 
each having a few very conspicuous characteristics in common, 
but smaller groupings have been made, each containing only 
a few plants having many characteristics in common. If we 
plant a number of peas so that they wiU all germinate under 
the same conditions of soil, temperature, and sunlight, the seed- 
lings that develop will differ one from another in a slight degree. 
But in a general way they will have many characteristics in 
common, as the shape of the leaves, the possession of tendrils, 
and the form of the flower and fruit. The smallest group of 
plants or animals having certain characteristics in common that 
make them different from all other plants or animals is called a 
species. Individuals of a species differ slightly; for no two 
individuals are exactly alike. 

A number of species are combined in a larger group called 
a genus (je'nus). For example, many kinds of peas — the garden 
peas, the wild beach peas, the sweet peas, and many others — 
are all grouped in one genus because they have certain structural 
characteristics in common. 

Plant and animal genera are brought together in still larger 
groups, the classification based on general likenesses in struc- 



134 FORMS AND REPRODUCTION OF PLANTS 



ture. Such groups are called, as they become successively larger, 
Family, Order, and Class. Thus the plant and animal kingdoms 
are grouped into divisions, the smallest of which contains indi- 
viduals very much alike; and the largest of which contains very 
many groups of individuals, each group having some charac- 
teristics in common. This is called a system of classification. 



CYMNOSPERMS ANQI05PERMS 



VERTEBRATA 



SPERMATOPHYTES 
I 
PTERIDOPHYTES 

BRY0PHYTE5 / 

\y FUNQI 

ALO/E 

BACTERIA 

THALL0PHYTE5 



MOLLUSCA 



INSECTA cpumCEA 



ECHINODERMATA 




PRIMITIVE OROANISMS 



Tree of life. There is little difference between the lowest forms of plant and ani- 
mal life, but much difference between the highest plants (Angiosperms) and the 
highest animals ( Vertebrata) . 

Classification of the Plant Kingdom. — The entire plant king- 
dom has been grouped as follows by botanists: 

Angiosperms (an'ji-6-spermzj, true flow- 
ering plants. 
Gymnosperms (jim'n6-spermz), the pines 
and their allies. 

2. Pteridophytes (ter'i-d6-f Its) . The fern plants and their allies. 

3. Bry'ophytes. Moss plants and their allies. 

i ^^9^f simple plants containing chlorophyll. 

4. ThaUophytes, | ^^^^^^ ^^^^^^ p^^^^^ without chlorophyll. 

The extent of the plant kingdom can only be estimated, be- 
cause each year new species are added to the lists. There are 



1. Sperrnatophytes. \ 



CLASSIFICATION OF PLANTS 135 

about 110,000 species of flowering plants and nearly as many 
flowerless plants. The latter consist of over 3500 species of 
fernlike plants, some 16,500 species of mosses, over 5600 lichens 
(li'kenz) — plants consisting of a partnership between algae and 
fungi, — • approximately 55,000 species of fungi, and about 16,000 
species of algse. Some botanists regard bacteria as fungi, while 
others make them a separate branch of thallophytes, as indicated 
in the diagram on page 134. 

Summary. — We have seen in this chapter that the diverse 
forms of plants on the earth may be grouped into four great 
divisions, the Thallophytes or very simple plants having a 
thallus body, the Bryophytes or mosses, Pteridophytes or ferns, 
and Spermatophytes or seed-producing plants. 

The environment has doubtless played a very important 
part in producing the various forms of plants, for botanists 
believe that many millions of years ago the earth was covered 
with a very much simpler vegetation than it is at present. 
Plants have been forced to adapt themselves to new conditions 
in order to live and varying conditions of environment have 
resulted in developing the different kinds of plants now existing. 

Problem Questions. — 1. How do changes in environment 
cause changes in plant structure? 

2. Why are the algae believed to be the first plants to in- 
habit the earth? 

3. How are algse of use to man? 

4. How can you distinguish a fungus? a moss? a fern? 

5. What is meant by alternation of generations? 

6. What is a species? 

7. What is meant by a system of classification? 

Problem and Project References 

Andrews, Botany All the Year Round, Chapter X. American Book Company. 

Conn, Bacteria, Yeasts and Molds of the Home. Ginn and Company. 

Coulter, Barnes and Cowles, A Textbook of Botany, Vol. I. American Book 

Company. 
Densmore, General Botany. Ginn and Company. 
Grout, Mosses with a Hand Lens. A. .J. Grout, New York City. 
Hunter, Laboratory Problems in Civic Biology. American Book Company. 
Parsons, How to Know the Ferns. Charles Scribner's Sons. 
Sedgwick and Wilson, General Biology. Henry Holt and Company. 
Underwood, Our Native Ferns and their Allies. Henry Holt and Company. 



XII. HOW PLANTS ARE MODIFIED BY THEIR 

SURROUNDINGS 

Problem, To discover how plants are modified by their suT' 
roundings. {Optional.) {Laboratory Manual, Prob. XXI.) 

(a) Hydrophytic society. (c) Mesophytic society, 

{b) Xerophytic society. {d) Plant societies. 

{e) Plant zonation. 

The Way in which Plants are modified by their Surround- 
ings. — As we have found in our experiments, young plants 

' are delicate organisms, 
which are affected pro- 
foundly by the action of 
forces outside themselves. 
The same is true to a 
certain extent of older 
plants. The presence or 
absence of moisture starts 
or prevents growth in 
seeds or young plants; 
absence of light changes 
the form and color of 
green plants; and favor- 
able temperature, which 
varies for different plants, 
influences the growth. 
Pea seedlings may grow 




Pond lilies, plants with floating leaves, 
graph by W. C. Barbour. 



Photo- 



for a time in sawdust, but we know that they will be much 
healthier and will live longer if placed in soil under natural 
conditions. We are forced to the conclusion that differences in 
the forms and habits of plants are caused by the action of their 
surroundings upon them. The plants which have become in 
various ways fitted to live under certain conditions are said to 
be adapted to such conditions. Such plants as are best fitted to 

136 



WATER SUPPLY 



137 



live under the conditions in which they are placed are the ones 
which will survive. 

Water Supply. ^- Water supply 
is one of the important factors in 
causing changes in structure of 
plants. Plants which live entirely 
in the water often have slender 
parts with finely divided leaves. 
Their roots are apt to be short and 
stout. The interior of such a plant 
is made up of spongy tissues which 
allow the air dissolved in the water 
in which they live to reach all 
parts of the plant. If the plant 
has floating leaves, as in the pond 
lily, the stomata are all in the 
upper side of the leaf. 

Hydrophytes. — When a plant lives in water or in soil satu- 
rated with water, the conditions of its environment are said to be 
hydrophyfic, and such plant is said to be a hydrophyte (hf dr6-fit). 

Xerophytes. — If we examine plants growing in dry or desert 




A water plant, showing the hiiely 
divided leaflike parts. 




A xerophyxic condition. Cacti and other plants in a desert. 
Photograph from American Museum of Natural History. 

HUNT. NEW ES. — 10 



138 PLAXTS MODIFIED BY THEIR SURROUXDIXGS 

conditions, as cactus, sagebrush, aloe, etc., we find that the leaf 
sui'face is invariabh^ reduced, sometimes forming spines as in the 
cactus. The stem may be thickened so as to store water; a cover- 
ing of hahs or some other material ma}^ be present and lessen 
the loss of moisture by evaporation. The conditions of extreme 
drjmess under which such plants live are called xerophytic (ze-r6- 
fit'ik), and such plants are known as xerophytes (ze'r6-fits). Ex^ 
amples of xeroph>i:es are the cacti, yuccas, centmy plants, etc. 
Halophytes. — If the water or saturated soil in which the 
plant lives contains salts, such as sea salt or the alkali salts of 




A mesophytic coiidition. A valley in central New York. 

some of our Western lakes, the conditions are said to be halo- 
phyt'ic, and a plant living under such conditions is known 
as a hal'ophyte. Haloph3i:es show mam^ characteristics which 
xeroph}i;es show. 

Mesophytes. — ^lost plants in the Temperate Zone occupy a 
place midway between the xerophytes on one hand and hj^di'o- 
phytes on the other. They are plants which require a moderate 
amount of water in the soil and air surrounding them. Such 
are most of our forest and fruit trees, and most of our gar- 



COLD REGIONS 



139 



den vegetables. Conditions of moderate moisture are called 
mesophytic; the plants living under such conditions are known 
as mesophytes (mes'6-fits). 

Other Factors. — It is a matter of common knowledge that 
plants in different regions of the earth differ greatly from one 
another in shape, size, and general appearance. If we study 
the causes for these changes, it becomes evident that the water 
supply is one of the most important factors, whether in the 















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The effect of wind upon trees in an exposed location. Photograph by W. C. Barbour. 

tropics or arctic regions. But in addition to water supply, the 
factors of temperature, light, soil, wind, etc., all play impor- 
tant parts in determining the form and structure of a plant. 

Cold Regions. — : Here plants, which in lowland regions of 
greater warmth and moisture have a tall form and luxuriant 
foliage, are stunted and dwarfed; their leaves are small and 
tend to gather in rosettes, or are otherwise closely placed for 
warmth and protection. As we climb a mountain we find that 
the average size of plants decreases as we approach the line of 



140 PLANTS MODIFIED BY THEIR SURROUNDINGS 

perpetual snow. The largest trees occur at the base of the 
mountain; the same species of trees near the summit appear 
as mere shrubs. Continued cold and high winds are evidently 
the factors which influence the slow growth and the small size 
and shape of plants near the mountain tX)ps. Cold, little light 
during the short days of the long winter, and a slight amount 
of moistm-e all act upon the vegetation of the arctic region, 




Polar limit of trees, northern Russia. All these trees are full grown, and most of 
_ them are almost one hundred years old. 



and tend to produce very slow growth and dwdrfed and stunted 
forms. 

Vegetation of the Tropics. — A rank and luxuriant growth is 
found in tropical countries with a uniformly high temperature 
and large rainfall. In general it may be estimated that the 
rainfall in such countries is at least twice as great as that of 
New York state, and in many cases three to four times as 
great. An abundant water supply, together with an average 
temperature of over 80° Fahrenheit, causes extremely rapid 
growth. One of the bamboo family,, the growth of which was 
measured daily, was found to increase in length on the average 
nearly three inches in the daytime and over five inches during 
each night. The moisture present in the atmosphere allows the 



VEGETATION OF THE TROPICS 



HI 



Cv^/^*^5^^ ; \ Region of Lichens. 

''^^^cf:^'i^-•- c r^'^^iNv Region of Grasses. 

^ ^-^^"^ **^^^^2:^"1^-^ Shrubby Region. 
LS|fV«ESM?'WiiV^'^" °^ Cinchona trees. 

/^oi ^^ p/" 953.^^^"^^*°^ ordinary large trees 

Plant regions in a tropical mountain. Explain the diagram. 

growth of many air plants {ep^iphytes), which take the mois- 
ture directly from the air by means of aerial roots. 

The absence of cold weather in tropical countries allows trees 
to mature without a thick coating of bark or corky material, 




Conditions in a moist, semitropical forest. The so-called "Florida moss" is a 
flowering plant. Notice the resurrection ferns on the tree trunk. 



142 PLANTS MODIFIED BY THEIR SURROUNDINGS 

and so they have a green and fresh appearance. Monocotyledo- 
nous plants prevail. Ferns of all varieties, especially the largest 
tree ferns, are abundant. 

Plant Life in the Temperate Zones. — In the state of New 
York, conditions are those of a typical temperate flora. Ex- 
tremes of cold and heat are found, the temperature ranging 
from 30° below zero Fahrenheit in the winter to 100° or over 




Plant societies near a pond. Notice that the plant groups are arranged in zones 
with reference to the water supply, the true mesophytes being in the background. 

in the summero Conditions of moisture show an average rain- 
fall of from 24 inches to 52 inches. 

In the eastern part of the United States the rainfall is suffi- 
cient to supply very extensive forests, which aid in keeping the 
water in the soil. In the Middle West the rainfall is less, the 
prairies are covered with grasses and other plants which have 
become adapted to withstand dryness. In the desert region of 
the Southwest we find true xerophytes, cacti, yuccas, and others, 
plants which are adapted to withstand almost total absence of 
moisture for long periods. In the Temperate Zone as elsewhere 
the water supply is the primary factor which determines the 
form of plant growth. 



PLANT FORMATIONS AND SOCIETIES 143 

Plant Formations and Societies. — All of the factors referred 
to act upon the plants we find living together in a forest, a 
sunny meadow, along a roadside, or at the edge of a pond. 
Any one familiar with the country knows instinctively that we 
find certain plants, and those plants only, living together under 
certain conditions. 

Plants ' associated under similar conditions, as those of a 
forest, meadow, or swamp, are said to make up a formation, 




A rock society. Photograph by W. C. Barbour. 

and a plant formation is brought about by the conditions of the 
immediate surroundings, the habitat of its members. If we in- 
vestigate a plant formation, we find it to be made up of certain 
dominant species of plants; that here and there definite com- 
munities exist, made up of groups of the same kind of plants. 
We can see that each one of these plant groups in the society 
evidently came originally from a single individual which flour- 
ished under the peculiar conditions of soil, water, light, etc., 
that were found in this spot. These single plants have evi- 
dently given rise to the members in each little family group, 
and thus have populated the locality. 

So we find among plants communal conditions similar to 
those of some animals. The many individuals of the com- 



144 PLANTS MODIFIED BY THEIR SURROUNDINGS 



munity live under similar conditions; they need the same sub- 
stances from the air, the water, the soil. They all need the 
light; they use the same food. Therefore there must be com- 
petition among them, especially between those near to each 
other. The plants which are strongest and best fitted to get 
what they need from their sm-roundings, live; the weaker ones 
are crowded out and die. 

But their lives are not all competition. The dead plants and 
animals give nitrogenous material to the living ones, from which 

the latter make living 
matter; some bacteria 
provide certain of the 
green plants with nitro- 
gen; many of the green 
plants make food for 
other plants lacking chlo- 
rophyll, while some algse 
and fungi actually Jive 
together in such a way 
as to be of mutual benefit 
to each other. The larger 
plants may shelter the 
smaller ones, protecting 
them from wind and storm, while the trees provide humus 
which holds the moisture in the ground, giving it off slowly to 
other plants. Animals scatter and plant seeds far and wide, 
and man may even start entire colonies in new^ localities. 

How Plants invade New Areas. — New areas are tenanted 
by plants in a similar manner. After the burning over of a 
forest, we find a new generation of plants springing up, often 
quite unlike the former occupants of the soil. First come the 
fireweed and other light-loving weeds, brought by means of 
their wind-blown seeds. With these are found patches of 
berries, the seeds of which w^re brought by birds or other ani- 
mals. A little later, quick-growing trees having seeds easily car- 
ried for some distance by the wind, like the aspen, or seeds often 
distributed by birds, as the wild cherry, invade the territory. 
Eventually we may have the area retenanted by the same 




A community of trilliums. Photograph by 
W. C. Barbour. 



HOW PLANTS INVADE NEW AREAS 



145 



kind of inhabitants as formerly, especially if the destruction of 
the original forest was not complete. 

In like manner, on the upper mountain meadows or by the 
sand dunes of the seashore, wherever plants place their out- 
posts, the advance is made from some thickly inhabited area, 
and this advance is always aided or hindered by agencies 




A plant outpost. The struggle here is keen. The advancing 
sand has killed the trees in the foreground. 

outside of the plant — ■ the wind, the soil, water, or animals. 
Thus the seeds obtain a foothold in new territory, and 
new lands are captured, held, and lost again by the plant 
communities. 

Summary. — Plants are so modified by the factors of their 
environment that they may take various forms and have many 
kinds of devices to enable them to cope with the unfavorable 
factors in their environment. Water plays a most important 
part in modifying their form and structure. Plants are grouped 
according to water supply, into xerophytic or drought-loving 
plants, hydrophytic or water-loving plants, and mesophytic 
plants or those which need a moderate supply of moisture. 
Different species of plants are usually found in definite associa- 
tions or groups. This grouping is brought about by the need 
of similar environmental conditions by different kinds of 
plants. 

Problem Questions. — 1. Why do plants vary in different 
localities? 



146 PLANTS MODIFIED BY THEIR SURROUNDINGS 

2. What are the chief structural differences between hydro- 
phytes, xeroph3i^es, and mesophj^tes? 

3. TMiat are the characteristics of tropical plants? of those 
from cold regions? 

4. How might a new outpost of plant life be established? 

Problem and Project References 

Andrews, Bof/iny All the Year Round. American Book Company. 

Clements, Plant Physiology and Ecology. Henry Holt and Company. 

Coulter, Plant Relations. D. Appleton and Company. 

Coulter, Barnes and Cowles, A Textbook of Botany, Vol. II. American Book 

Company. 
Hunter, Laboratory Problems in Civic Biology. American Book Company. 
Kerner, Natural History of Plants. Henry Holt and Company. 
Schimper, Plant Geography. Clarendon Press. 



XIII. HOW PLANTS BENEFIT AND HARM 

MANKIND 

Problem, To determine how fungi help or harm mankind. 
(Laboratory Manual, Prob. XXII; Laboratory Problems, Probs. 
87 to 94.) 

(a) Yeast. 

(b) Mold. 

(c) Other fungi. 

The Economic Value of Plants. — Besides the other relations 
existing between plants and animals, there is a relation between 
man and plants measurable in dollars and cents. Plants are of 
direct value or harm to man. We call this an economic relation. 
We have seen how they supply him with his cereals and flour, 
his fruits and garden vegetables, his nuts and spices, his bever- 
ages and the sugar to sweeten them, his medicines and his dye- 
stuffs. They supply the material out of which many of his 
clothes are made, the thread with which they are sewed to- 
gether, the paper which covers the package in which they are 
delivered, and the string with which the package is tied. The 
various uses of the forest have been mentioned before; the 
need of trees to protect the earth, their usefulness in regulating 
the water supply, and their direct economic importance for 
lumber and firewood. Many of us forget, too, that much of 
the energy released on this earth to man as heat, light, or mo- 
tive power comes from the dead and compressed bodies of 
plants which thousands of years ago lived on the earth and now 
form coal. Plants are thus seen to be of immense direct eco- 
nomic importance to mankind. 

The Harm Plants Do. — Unfortunately, plants do not all 
benefit mankind. We have seen the harm done by weeds, 
which scatter their numerous seeds far and wide or by other 
devices gain a foothold and preempt the territory which useful 
plants might occupy were they able to cope with their better- 

147 



148 HOW PLANTS BENEFIT AND HARM MANKIND 



equipped adversaries. Plants with poisonous seeds and fruits 
are undoubtedly responsible for the death of many animals and 
of man as well. 

But the plants by far the most harmful to mankind are the 
fungi. Damage to the amount of hundreds of millions of dol- 
lars a year may be laid directly to them. More than that, if 
we include the tiny organisms called bacteria they are respon- 
sible for over one half of the total human deaths, because of 
their parasitic habits. 

Yeast. — Although as a group the fungi are harmful to man 
in the economic sense, nevertheless there are some fungi that 
stand in a decidedly helpful relationship to the human race. 
Chief of these are the yeast plants. Yeasts are found to exist 
in a wild state in very many parts of the world. They aTe 
found on the skins of apples, grapes, and other fruits, and they 
may exist in a dry state almost anywhere in the air around us. 
In a cultivated state we find them as the agents which cause 
the rising of bread, and the fermentation in beer and other 
alcoholic fluids. 

Yeast Plants. — ■ The common compressed yeast cake contains 
millions of these tiny plants. In its simplest form a yeast plant 

is a single cell. If you shake 
up a bit of a compressed yeast 
cake in a mixture of molasses 
and water and then examine 
a drop of the milky fluid after 
it has stood over night, it will 
be seen to contain vast num- 
bers of yeast plants. The 
plants are tiny ovoid cells 




from 



1 

2500 



to 



of 



an 



1 0,000 

Budding yeast plants stained to show j^ch in diameter. The pro- 
nucleus, highly magnified. . 

toplasm IS granular and con- 
tains no chlorophyll. The cells grow by means of budding, the 
parent cell forming one or more daughter cells somewhat smaller 
than the original cell and attached to it (see Figure). Some- 
times yeast cells form spores, although we rarely see them in 
the laboratory. 



FUNGI 149 

Conditions Favorable to Growth of Yeast. — Under certain 
conditions yeast, when added to dough, will cause it to rise. 
We know also that yeast has something to do with the process 
of fermentation. The following home experiment will throw 
some light on these points: 

Label three pint fruit jars A, B, and C. Add one fourth of a compressed 
yeast cake to two cups of water containing two tablespoonfuls of molasses. 
Stir the mixture well, divide it into three equal parts, and pour one part 
into each jar. Place covers on the jars. Put jar A in the ice box on the 
ice, and jar B over the kitchen stove or near a radiator; heat jar C by 
immersing it in a dish of boiUng water, and place it next to B. After 
forty-eight hours, look to see if any bubbles have made their appearance in 
any of the jars. If the experiment has been successful only jar B will show 
bubbles. After bubbles have begun to appear at the surface, the fluid in 
jar B will be found to have a sour taste and will smell unpleasantly. The 
gas which rises to the surface, if collected and tested, will be found to be 
carbon dioxide. The contents of jar B are said to have fermented. Evi- 
dently, the growth of yeast will take place under conditions of moderate 
warmth and moisture and in the presence of food. 

Fermentation a Chemical Process. — In the growth of yeast 
cells the sugar of the solution in which they live is broken 
up by an enzyme into carbon dioxide and alcohol. This may 
be expressed by the following chemical formula: C6II12O6 = 
2(C2H60) + 2(C02). This means that the sugar acted upon 
by the enzyme in the yeast cell, is made into alcohol and car- 
bon dioxide. This process is called fermentation. 

When bread dough is expected to " raise "it is put in a warm 
place so that the yeast plants in the dough will grow rap- 
idly. They feed upon starch, which they digest into grape 
sugar. Fermentation results from the rapid growth, causing 
the bubbles of carbon dioxide in the dough. When the bread is 
baked the spaces which were filled with carbon dioxide remain 
while the alcohol is evaporated in the baking. 

The Yeast Plant a Saprophyte. — Since yeast grows upon 
dead organic material it is a saprophyte. Saprophytic plants 
are frequently seen in our homes and some do much damage. 
Bread mold is an example. 

Mold. — This is one of our most common fungi. It grows 
upon bread, cake, and other organic substances under certain 
conditions of temperature and moisture. 



150 HOW PLANTS BENEFIT AND HARM MANKIND 

We are all familiar with the tangled mass of tiny whitish 
threads which are sometimes found growing over damp bread. 
The mass of threads is called collectively the mycelium 
(mi-se'li-mn), each thread being called a hypha (hi'fa). 
Many of the hyphse are prolonged into tiny, upright 
threads, bearing a little ball at the top. With the low power 
microscope each of these structures is seen to contain many 




Stages in reproduction of mold: A, vegetative form, showing the rootlike 
rhizoids r, the mycelium m, and the spore-bearing bodies s, in three stages of growth; 
B to E, stages in conjugation, resulting in the formation of a zygospore z. 

tiny bodies called spores. These spores have been formed 
by the division of the protoplasm within the ball or sporan- 
gium into many separate bodies or asexual spores. These 
spdres, if grown under favorable conditions, will produce more 
mycelia, which in turn bear sporangia. The mold, however, 
like spirogyra, can produce zygospores under certain conditions. 
These are probably sexual spores and are evidently of use to 
continue the life of the plant during unfavorable conditions. 
Physiology of the Growth of Mold. — Mold, in order to grow 
rapidly, evidently needs oxygen, moisture, and a favorable tern- 



FUNGI 



151 



perature. The mold sends down into the bread rootHke proc- 
esses. These branching hyphse pass out through their walls 
digestive enzymes, which change the starches and proteins of 
the bread to soluble substances which are taken in through the 
walls of the hyphse by osmosis. Thus a mold digests its food 
outside of the body and then absorbs it. These foods are then 
used to supply energy and to make protoplasm. This seems to 
be the usual method by which saprophytes secure the ma- 
terials on which they live. 

Other Saprophytic Fungi : Mushrooms. — Some of the best 
known of the fungi are the mushrooms or '^ toadstools " as they 
are often called. What we 
see is the temporary spore- 
bearing part, the mycehum 
being below ground. The 
mushrooms live upon decay- 
ing plant or animal material, 
which they digest and absorb 
by means of their rootlike 
hyphse. Care and good judg- 
ment are needed in distin- 
guishing the harmful from 
the edible mushrooms, al- 
though it is not hard to learn 
some of the edible fungi of a 
locality. Why not make this 
a project to work out? Ex- 
cellent books of reference 
on this subject are Marshall's 
The Mushroom Book, Double- 
day, Page and Company, and 
Atkinson's Mushrooms, Henry Holt and Company. 

The Shelf Fungus. — This is a near relative of ' the mush- 
room. The " bracket " found growing on dead tree trunks is 
the spore case, while the mycelium is within the tissue of the 
tree. Remove the bark from a tree infected with a bracket 
fungus, and you will find the silvery threads of the mycelium 
sending their greedy hyphae to all parts of the wood adjacent 




Mushiooms; the ^'oinitj.er specimen, at 
the right, shows some of the mycelium. 
Photographsd by Overton. 



152 HOW PLANTS BENEFIT AND HARM MANKIND 

to the spot first attacked by the fungus. This fungus begins 
its Hfe by the lodgment of a spore in some part of the tree 
which has become diseased or broken. Once estabhshed on its 
host, it spreads rapidly. Each year many fine trees, sound 
except for a slight bruise or other injury, are infected and 
eventually killed. In cities thousands of trees become infected 
where horses have been hitched carelessly so that they could 
gnaw or crib on the tree, thus exposing a fresh surface on 
which spores may obtain lodgment and grow (see page 123). 
There is no remedy except to burn the infected trees, so as to 
destroy the spores. 

Suggestions for Field Work. — A field trip to a park or grove near home 
may show the great destruction of timber by this means. Count the num- 
ber of perfect trees in a given area. Compare it with the number of trees 
attacked by the fungus. Does the fungus appear to be transmitted from 
one tree to another near at hand? In how many instances can you dis- 
cover the point where the fungus first attacked the tree? How do the 
spores leave the sporecase? How do they germinate on the tree attacked? 

Parasitic Fungi. — Of even more importance are the fungi 
that attack a living host, true parasites. The most important 
of such plants from an economic standpoint are the rusts, 
smuts, and mildews which prey upon grain, corn, and other cul- 
tivated plants. Some fungi are also parasitic upon fruit and 
shade trees. The chestnut canker, a fungus introduced from 
abroad on chestnuts planted near the city of New York in 
1904, had during ten years destroyed practically every chest- 
nut tree within a radius of 150 miles. At the present time the 
disease is spreading rapidly and may eventually destroy all of 
the native chestnuts in the United States unless di'astic meth- 
ods of combating the pest are used. Hundreds of millions of 
dollars' damage has already been done and more will follow. 
The pine tree blister rust introduced from Europe about 1909 
threatens the existence of nearly $500,000,000 of timber. 

Wheat Rust. — Wheat rust is probabl}^ the most destructive 
parasitic fungus. For hundreds of years this rust has been 
the most dreaded of plant diseases, because it destroys the one 
harvest upon which the civilized world is most dependent. For 
a long time past the appearance of rust has been associated with 



FUNGI 153 

the presence of barberry bushes in the neighborhood of the 
wheat fields. Although laws were enacted in 1760 in New Eng- 
land to provide for the destruction of barberry bushes near 
infected wheat fields, nothing was actually known of the rela- 
tion existing between the rust and the barberry until compara- 
tively recent years. It has now been proved beyond doubt that 
the wheat rust passes part of its life as a parasite on the barberry 
and from it gets to the wheat plant, where it undergoes a com- 
plicated life history. The wheat leaf, its nourishment and liv- 
ing matter used as food by the parasite, soon dies, and no grain 
is produced. Some wheat rusts appear to have other intermediate 
hosts than the barberry, so that the problem of fighting this plant 
enemy has been much more difficult than if all the facts about it 
were known. 

Sac Fungi. — Another group of fungi that are of considerable 
economic importance is made up of the sac fungi. Some of these 
fungi are called mildews. Some of the most easily obtained 
specimens come from the lilac, rose, or willow. These fungi 
do not penetrate the host plant to any depth, but cover the 
leaves of the host with the whitish threads of the mycelium. 
Hence they may be killed by means of applications of some 
fungus-killing fluid, as Bordeaux mixture. They obtain their 
food from the outer layer of cells in the leaf of the host. Among 
the useful plants preyed upon by this group of fungi are the 
plum, cherry, and peach trees. The diseases known as black 
knot and peach curl are thus caused. 

Problem, A study of bacteria in order to determine — 

(a) Their conditions of growth. 

(b) Some of their relations to man. 

(c) Methods of fighting harmful bacteria. 

(Laboratory Manual, Prob. XXIII; Laboratory Problems, 
Probs. 95 to 103.) 

Bacteria. — The bacteria are found in the earth, the water, 
and the air: '' anywhere but not everywhere,'' as one writer 
has put it. They swarm in stale milk, in impure water, in the 
living bodies of plants and animals, and in any decaying 
material. These tiny plants, ^' man's invisible friends and foes," 

HUNT. NEW ES. — 11 



154 HOW PLANTS BENEFIT AND HARM MANKIND 



are of such importance to mankind that thousands of scientists 
devote their whole Hves to the study of bacteriology. 

How Bacteria were Discovered. — As early as 1683 the 
Dutchman Leeuwenhoek is believed to have seen bacteria with 
his newly invented microscope. But it was not until 1865 
that Louis Pasteur, the famous Frenchman, discovered the rela- 
tion between bacteria and disease. Pasteur had shortly before 
this proved that bacteria caused fermentation and that when 
floating germs got into nutrient fluids such fluids would " go 
bad '' and would decay. Pasteur laid the foundation for the 

study of disease germs and his name should 
be remembered, not alone for his discovery 
of a cure for hydrophobia but because he 
was the first man to attempt to manufacture 
antitoxin serums and vaccines to fight the 
poisons produced by disease. Robert Koch is 
another man who helped to make bacteri- 
ology an important science. We remember 
him in particular as the discoverer of the 
germ causing tuberculosis. 

Size and Form. — Bacteria are the most 
minute organisms known. A bacterium of 
average size is about -g-^^ of an inch in 
length, and perhaps ^^ oqq of an inch in 
diameter. Some species are much larger, 
others smaller. A common spherical form 
is .^ L» of an inch in diameter. It will 




Bacteria, highly mag- 
nified: a, the germ of 
typhoid fever, stained 
to show the cilia, little 
threads of living matter 
by means of which lo- 
comotion is accom- 
plished; b, a spiral 
form with flagella, tiny ^^ 50,000 

threads longer than mean more to US, perhaps, if we realize that 



cilia ; c, a rod-shaped 
form, in a chaia ; d, a 
spherical form. 



1000 bacteria of average size might be placed 
on the dot of this letter i. Three well- 
defined forms of bacteria are recognized : a spherical form called 
a coc'cus; a rod-shaped bacterium, the bacillus (ba-sil'us); and a 
spiral form, the spiriVlum. Some bacteria are capable of move- 
ment when living in a fluid. Such movement seems to be 
caused by tiny threads of protoplasm called cilia or flagella, which 
project from the body and vibrate rapidly. Bacteria reproduce 
with almost incredible rapidity. A single bacterium, by simple 
fission or splitting, will in twelve hours give rise to almost 



BACTERIA 



155 



17,000,000 offspring if each divides only once every half hour. 
It has been estimated that if a bacterium could go on multi- 
plying unchecked for five days, it would fill all the oceans of 
the earth to a depth of one mile. But of course nothing of the 
kind ever happens because of the many unfavorable conditions 
which exist. Under unfavorable conditions bacteria die or at 
least stop dividing and form spores, in which state they remain 
until conditions of temperature and moisture are such that 
growth may begin again. 

Method of Study. — In order to get a group of bacteria of a 
given kind to study, it becomes necessary first to catch them. 
This is easily done by expos- 
ing to the air a shallow dish — 
known as a Petri (pet're) 
dish — containing a culture 
medium on which bacteria 
will grow. The medium is 
made by cooking beef broth 
and either gelatine or agar- 
agar together for a few mo- 
ments. The culture medium 
is poured into a sterilized 
Petri dish while it is still hot 
and the cover is placed over 
it quickly so that the con- 
tents of the dish will remain 
sterile or free from all life 
until the cover is removed. If after a short exposure to the air 
of the schoolroom the dish is covered and put away in a warm 
place for a day or two, little spots will appear on the surface 
of the culture medium. 

Pure Culture. — The spots are colonies composed of millions 
of bacteria. If now we wish to study one given form, it becomes 
necessary to isolate it from the others in the dish. This is done 
by the following process: a platinum needle is first passed 
through a flame to sterilize it; that is, to kill all Hving things 
that may be on the needle point. Then the needle, which cools 
very quickly, is dipped in a colony containing the kind of bac- 




A Petri dish culture of bacteria; the 
colonies of bacteria are little spots of 
various sizes and colors. 



loG HOW PLANTS BENEFIT AND HARM .MANKIND 

teria we wish to study. This mass of bacteria is qiiickh' 
transferred to another steriUzed Petri dish containing cultui'e 
mediumj and covered to prevent any other forms of bacteria 
from entering. The dish is then placed in a warm oven for a 
night in order to get a good gi'owth of bacteria. Wlien we have 
succeeded in isolating a certain kind of bacteria in a given dish. 
that is, when colonies of only one kind are present, we have a 
pure culture. 

Conditions Favorable and Unfavorable for Growth of Bacteria. 
— Temperature. Like most h^ing things, bacteria grow most 
rapidly in a favorable temperature, "^liile this is usually about 
body temperature or 98.6° Fahrenheit, it is sometimes lower. 
We may saj^ that at this favorable temperature bacteria have 
the most rapid growth. Conversely, cold retards their growth, 
as does extreme heat. Freezing will stop their growth alto- 
gether, although it does not kill the more hardy fonns. Heating 
to 150~ to 160" Fahrenheit will, if continued for at least thirty 
minutes, destroj' bacteria with the exception of those in the 
spore stage. These may resist boihng for some time. In order 
to make absolutely sure that all spores are killed, the bacteri- 
ologist raises the material which contains them to boihng for 
a second or even a thu'd time, with a period of several hours 
intervening in each case. This is known as discontmuous 
sterilization. 

Moisture. Bacteria requu'e considerable moistm^e in order to 
grow, although they may be found in an inactive state in drj- 
locahties. Household foods, therefore, if in a diy condition, 
will not be spoiled bj^ bacteria, a fact worth remembering. 

Light. We find that if a Petri dish containing growing bac- 
teria is exposed to a strong light the growth will be retarded 
or stopped completely. Simlight kills many kinds of bacteria. 
This fact has been made use of in the fight against various 
disease-producing bacteria, especially those which produce tu- 
berculosis. A sickroom should therefore be flooded with sun- 
light whenever possible, and should be provided with fm'niture 
and hangings that can easily be cleaned and aii-ed. 

Air. Although bacteria need oxygen in order to live, as do 
all living things, some kinds thrive in the absence of air, ob- 



BACTERIA 



157 



taining the oxygen necessary for oxidation by breaking down 
the substances on which they feed, thus releasing oxygen. 
Such bacteria are called anaerobic (an-a-er-6b'ik). Most of the 
bacteria found in daily life live in the air and are called aerobic. 

Bacteria cause Decay. — Bacteria affect mankind in many 
ways, either directly or indirectly. First of all, they cause 
decay. All organic matter, in whatever form, is sooner or later 
decomposed by the action of untold millions of bacteria which 
live upon organic matter in water and soil. These bacteria, 
therefore, are useful because they feed upon the dead bodies 
of plants or animals, which otherwise would soon cover the 
surface of the earth to the 
exclusion of everything else. 
Bacteria may thus be con- 
sidered scavengers. Without 
bacteria and a few of the 
fungi, life on the earth would 
be impossible, for green plants 
would be unable to get the 
raw materials in forms that 
they could use in making 
food and new living matter. 
In this respect bacteria are 
of the greatest service to 
mankind. 

When bacteria grow in suffi- 
cient numbers upon foods, 
meat, fish, or vegetables, they 
spoil them, and may form 
poisonous substances called 
ptomaines (to'-ma-inz) by 
their action on protein. As 
the result of eating food con- 
taining these ptomaine poisons, one may become violently ill. 
Fish and meats that have been kept for some time in cold 
storage are very easily spoiled, and should be avoided. Canned 
goods that have " worked," that is, those in which yeasts or 
bacteria have caused fermentation and decay, are unfit for food. 




Tubercles or nodules (little lumps) on 
the roots of soy bean, containing nitrogen- 
fixing bacteria. 



158 HOW PLANTS BEXEFIT AXD HAR:\1 MANKIND 



Nitrogen-fixing Bacteria. — Certain bacteria, in the process of 
decay, ^' change over " nitrogen in organic material in the soil 
so that it can be used by plants in the form of a compound of 
nitrogen. But the bacteria living in tubercles on the roots of 

clover, beans, peas, etc., 
have the power of ''fixing" 
the free nitrogen in the au' 
found between pai'ticles of 
soil so that it may be ab- 
sorbed as a nitrate bj^ the 
root hah. This fact is made 
use of bj^ farmers who rotate 
'^ theh crops, gi'owing first a 
crop of clover or alfalfa, 
which produce the bacteria, 
then plowing these up and 




A pasteurizing apparatus. 



planting another crop, as wheat or corn, on the same area. The 
latter plants, making use of the nitrogen compounds there, pro- 
duce a larger crop than when 
grown in ground containing 
less nitrogenous material. 

Other Processes caused 
by Bacteria. — Bacteria may 
incidentally, as a result of the 
process of decay, aid in the 
process of feiTaentation. In 
making vinegar the yeasts first 
make alcohol (see page 149). 
which the bacteria later 
change to acetic acid. In 
milk there are many kinds of 
bacteria, some of which act 
upon the milk sugar, changing 
it to an acid, and thus caus- 
ing the milk to sour. The 
lactic acid bacteria grow very 
rapidly in a warm temperature; hence milk which is kept iced 
does not sour readily. Pasteurized milk (that is, milk that has 




Microscopic appearance of ordinary 
milk, showing fat globules and bacteria. 
The cluster of bacteria on the right side 
are germs that form lactic acid. Tubercu- 
losis germs are sometimes found in milk. 



BACTERIA 



159 



been heated to a temperature of about 145° Fahrenheit for 
20 or 30 minutes) remains sweet for some time also if kept in a 
cool place. Why ? The same lactic acid bacteria may be useful 
when they sour the milk for the cheese-maker. Certain other 
bacteria give flavors to cheese and butter, while still others are 
used by the tanner in the preparation of leather. The '' ret- 
ting '' of flax, or the rotting away of the non-usable tissues of 
the flax stem, is due to the action of bacteria. Sponges are pre- 
pared for the market by bacteria which decompose the sponge 
tissues, leaving the skeleton behind. Bacteria are, after all, 
often very useful. But in spite of the good they do, their 
harmfulness is manifest, for they cause diseases, many of which 
are " catching " or infectious. 

Bacteria cause Disease. — Certain bacteria cause disease by 
living as parasites in the human body. Millions upon millions of 
bacteria exist in the 
human body at all 
times — in the mouth, 
on the teeth, and es- 
pecially in the lower 
part of the food tube. 
Some in the food tube 
are believed to be use- 
ful, others harmless; 
still others cause decay 
of the teeth, while a few 
kinds, if present on the 
roots of the teeth, may 
cause disease. 

It is known that 
bacteria, like all other 
living things, feed and 
give off organic wastes. 
These wastes, called toxins, are often poisons to the hosts on 
which the bacteria live, and it is usually the production of a 
toxin that causes the symptoms of disease. Some bacteria, 
however, break down tissues and plug up the small blood 
vessels, thus causing symptoms of disease. 




A single cell scraped from the roof of the mouth 
and highly magnified. The little dots are living 
bacteria, most of them comparatively harmless. 



160 HOW PLANTS BENEFIT AND HARM MANKIND 

Diseases caused by Bacteria. — It is estimated that bacteria 
cause annually over 50 per cent of the deaths of the human 
race. As we shall see later, a very large proportion of these 
diseases might be prevented if people were educated sufficiently 
to take the proper precautions to prevent their spread. These 
precautions might save the lives of some 3,000,000 people 
yearly in Europe and America. Tuberculo'sis, typhoid fever, 
diphtheria (dif-the'ri-a), pneumonia (nu-mo'ni-a), biood poison- 
ing, syphilis (sif'i-lis), and a score of other ^' germ " diseases 
ought not to exist. A good deal of the present misery of this 
world might be prevented and this earth made cleaner and bet- 
ter by the cooperation of the young people now growing up to 
be our future home-makers. 

How Germs get into the Body. — Germs of contagious diseases 
enter the body either by way of the mouth, nose, or other 
body openings or through a break in the skin. They leave the 
body of an infected person with the excretions, especially those 
from the nose, mouth, and intestine. They may be carried by 
means of air, food, or water, and are usually acquired from the 
diseased person either by personal contact, by handUng articles 
used by the sick, or by using foods which have been infected. 
Most germ diseases start with running at the nose, cough or 
sore throat, shght fever or headache. If children and grown-ups 
who have these symptoms could be kept away from other peo- 
ple, many an outbreak of contagious disease would be avoided. 

Tuberculosis. — The one disease responsible for the greatest 
number of deaths — about one tenth of the total on the 
globe — is tuberculosis. But this disease is slowly but surely 
being overcome. It is believed that within perhaps fifty j^ears 
with the application of the knowledge that every high-school 
boy and girl now has and with the additional aid of good laws 
and of sanitary living, it will be almost extinct. 

Tuberculosis is caused by the growth of bacteria, called 
tubercle bacilli, within the lungs or other tissues of the human 
body. In the lungs they form little tubers full of germs, which 
close up the delicate air passages. In other tissues tliey may 
give rise to hip-joint disease, scrofuki, lui)us, and other diseases, 
depending on the part of the body attacked. Many beUeve 



BACTEUIA 



161 



that tuberculosis may be contracted by eating meat or drinking 
milk from tubercular cattle. It is most often communicated 
from a consumptive (tuberculous) to a well person by kissing, 
or by using the same cup, plate, towels, or by spraying the germs 
from the mouth of the consumptive out into the nose or mouth 
of another person by coughing, sneezing, or even talking close to 
his face. Although there are always some tuberculosis germs in 
the air of an ordinary city street, and although we may take 
some of these germs into our bodies at any time, yet the bac- 
teria seem able to gain a foothold only under certain conditions. 
It is only when the tissues are in a worn-out condition, when 
we are " run down,'' as we say, that the parasite may obtain 
a foothold in the lungs. Even if the disease gets a foothold, 




How sewage containing typhoid bacteria may get into drink- 
ing water: c, cesspool. 

it is quite possible to cure it if it is taken in time. The germ 
of tuberculosis is killed by exposure to bright sunlight and 
fresh air. Thus the course of the disease may be arrested, and 
a permanent cure brought about, by a life in the open air, the 
patient sleeping out of doors, taking plenty of nourishing food 
and very little exercise. (See also Chapter XXX.) 

Typhoid Fever. — One of the most common germ diseases in 
this country and Europe used to be typhoid fever. This is a dis- 
ease which is conveyed by flies and by water and food, especially 
milk, oysters, and uncooked vegetables. Typhoid fever germs 
live in the intestine, where they multiply verv rapidly and are 



162 HOW PLANTS BENEFIT AND HARM MANKIND 

passed off from the body with the excreta from the food tube. 
If these germs get into the water supply of a town, an epidemic 
of typhoid will result. Among the epidemics caused by the 
use of water containing typhoid germs have been those in 
Butler, Pa., where 1364 persons were made ill; Ithaca, N.Y., 
with 1350 cases; and Watertown, N.Y., where over 5000 
cases occurred. Fortunately most water supplies of cities 
are now made safe by filtration and chlorina'tion. (See 
Chapter XXX.) Another source of infection is milk. Fre- 
quently epidemics have occurred which were confined to 
users of milk from a certain dairy. Upon investigation it was 
found that a case of typhoid had occurred on the farm where 
the milk came from, that the germs had washed into the well, 
and that this water was used to wash the milk cans. Once in 
the milk, the bacteria multiplied rapidly, so that the milkman 
gave out cultures of typhoid in his milk bottles. Pasteurisation 
and proper inspection of our milk supply are necessary if we are 
to prevent epidemics of typhoid under the present conditions. 
The only sure way to keep from having the disease is to be 
vaccinated against typhoid. (See Chapter XXX.) 

Tetanus. — The bacterium causing tet'anus, or blood poisoning, 
is another toxin-forming germ. It lives in the earth and enters 
the body through cuts or bruises. It seems to thrive best in 
less oxygen than is found in the air. It is therefore important 
not to close up with court-plaster wounds in which such germs 
may have found lodgment. 

Other Diseases. — Many other diseases have been traced to 
bacteria. Diphtheria is one of the best known. As it is a throat 
disease, it may easily be conveyed from one person to another 
by kissing, putting into the mouth objects which have come in 
contact with the mouth of a patient having diphtheria, or by 
food into which the germs have found their way. Septic sore 
throat is another disease which is easily spread through milk 
supplies, as is scarlet fever. The venereal diseases, gonorrhoea 
and syphilis, probably cause more misery than any other germ 
diseases. They cause hundreds of thousands of children to be 
born crippled, blind, or otherwise handicapped for life and are 
responsible for the deaths of many young mothers. Grippe, 



BACTERIA 163 

pneumonia, whooping cough, and colds are believed to be 
caused by bacteria. But other diseases, as malaria, yellow fever, 
sleeping sickness, and probably smallpox, scarlet fever, and 
measles, are due to the attack of one-celled animal parasites. Of 
these we shall learn later in the chapter on Protozoa. 

Methods of fighting Germ Diseases. — As we have seen, dis- 
eases produced by bacteria may be caused by the bacteria being 
transferred from one person directly to another, or the disease 
germs may gain an entrance into the body with food, water, or 
air, or by taking them into the blood through a wound or a 
body opening. 

It is evident that as individuals we may each do something 
to prevent the spread of germ diseases, particularly in our homes. 
We may keep our bodies, especially our hands and faces, clean. 
Green soap and hot water are as good cleansing agents as we 
can get. Sweeping and dusting may be done with damp cloths 
so as not to raise a dust; water, when from a suspicious supply, 
should be sterilized, — that is, boiled to kill any germs contained 
in it, — and milk should be pasteurized. 

Uses of Antiseptics. — About the year 1867, an Edinburgh 
surgeon. Lister, decided that germs floating in the air entered 
wounds and caused blood poisoning among his hospital patients. 
So he began washing their wounds with weak carbolic acid and 
covering them with gauze wet with carbohc acid. In a short 
time he proved to the world the value of antisep'tics or materials 
that prevent bacteria from growing. We have largely given up 
carboHc acid to-day and use iodine for cuts or bruises. For sore 
throat argyrol (15 per cent) is best; for inflamed eyes a saturated 
solution of boracic acid is good; while an excellent mouth wash 
is salt and warm water (about a half-teaspoonful of salt to a 
cup of water). 

Summary. — The knowledge gained from the study of this 
chapter should be of much practical value to every boy and girl. 
We have seen that green plants not only have a decided eco- 
nomic value in producing foods, medicines, dyestuffs, clothes, 
paper, lumber, and fuel, but they also regulate our water 
supplies, moderate our climate, and use that greatest source of 
energy, the sun, for man's good. 



164 HOW PLANTS BENEFIT AND HARM MANKIND 

The plants without chlorophyll may be harmful, or harmless 
or valuable. Some, like the yeasts, are of definite use in the 
process of fermentation antl bread making; others, the molds, 
have a slight value but do more harm than good in spoiling 
food. The third great group, the bacteria, are man's greatest 
friends as well as his most deadly foes. Without them decay 
would not take place — try to unagine life on the earth with 
no way to get rid of dead matter. They also give flavor to 
cheese and milk, and to other foods; they are useful in the 
tanner's trade as well as in many other kinds of work where 
decomposition plays a part. And the fertility of the soil depends 
upon certain kinds of bacteria, especially those which " fix " 
free nitrogen from the air. 

On the other side of the scale we can pile up a great weight 
against the bacteria. Probably nearly 75 per cent of all people 
on the earth die of diseases caused by bacteria and other parasites 
which could have been prevented. The great mortality among 
young children is due largely to bacteria causing diarrhea, the 
tuberculosis germ is responsible for over one tenth of all the 
deaths on the earth, while pneumonia, influenza, typhoid, ve- 
nereal diseases, and many others either kill or weaken people 
so that many die before reaching the threescore years and ten 
allotted to them. This chapter and the ones which treat of 
health and our civic obligations (XXIX and XXX) are among 
the most important in the book for us. 

Problem Questions. — 1. What are some of the uses of green 
plants not mentioned in this chapter? 

2. VThy do the farmers need bacteria? ^lention all the waj^s 
in which they are useful. 

3. In what ways do farmers need to guard against bacteria? 

4. In what trades are yeasts useful? Harmful? 

5. In what trades are molds useful? 

6. Do bacteria do more harm or good? Give reasons for 
both sides of your argument. 

7. "WTiat specific diseases have you been able to find caused 
by bacteria? 

8. WTiat methods would you use to prevent " taking " an 
infectious disease? 



BACTERIA • 165 

9. What are the best methods of controlling the growth of 
bacteria ? 

Problem and Project References 

Broadhurst, Home and Community Hygiene. J. B. Lippincott Company. 

Conn, Bacteria, Yeasts, and Molds of the Hom.e. Ginn and Company. 

Conn, Story of Germ Life. D. Appleton and Company. 

Davison, The Human Body and Health. American Book Company. 

Frankland, Bacteria in Daily Life. Longmans, Green, and Company. 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Hunter and Whitman, Civic Science. American Book Company. 

Locy, Main Currents of Zoology. Henry Holt and Company. 

McCarthy, Health and Efficiency. Henry Holt and Company. 

Prudden, The Story of the Bacteria. G. B. Putnam's Sons. 

Ritchie, A Primer of Sanitation. The World Book Company. 

Sedgwick, Principles of Sanitary Science and Public Health. The Macmillan 

Company. 
Sharpe, A Laboratory Manual. American Book Company, 



XIV. THE RELATIONS OF PLANTS TO ANIMALS 

Problem, To discover the general biological relations existing 
between plants and animals. {Laboratory Manual, Prob. XXIV; 
Laboratory Problems, Probs. 108 to 111,) 

(a) A balanced aquarium, 

(6) Relations between green plants and animals* 

(c) The nitrogen cycle, 

(d) A hay infusion. 

Study of a Balanced Aquarium. — Perhaps the best way for 
us to understand the interrelation betvv^een plants and animals 
is to study an aquarium in which plants and animals live and 
in which a balance has been established between the plant life 
on one side and animal life on the other. Aquaria containing 
green pond weeds, either floating or rooted, a few snails, some 
tiny animals known as water fleas, and a fish or two will, if kept 
near a Hght window, show this relation. (See Frontispiece.) 

We have seen that green plants under favorable conditions 
of sunlight, heat, moisture, and with a supply of raw food 
materials, give off oxygen as a by-product while manufacturing 
food in the green cells. We know the necessary raw materials 
for starch manufacture are carbon dioxide and water, while 
nitrogenous material is necessary for the making of proteins 
within the plant. In previous experiments we have proved that 
carbon dioxide is given off by any living thing when oxidation 
occurs in the body. The crawling snails and the swimming fish 
give off carbon dioxide, which is dissolved in the water; the 
plants themselves, night and day, oxidize food within their 
bodies, and so must pass off some carbon dioxide. The green 
plants in the sunlight use up the carbon dioxide obtained from 
the various sources and, with absorbed water, manufacture 
starch. While this process is going on, oxygen is given off to 
the water of the aquarium, and this is used by the animals. 

But the plants are continually growing larger. The soaUs aud 

166 



RELATIONS BETWEEN PLANTS AND ANIMALS 167 



fish, too, eat parts of the plants. Thus the plant life gives food 
to part of the animal life within the aquarium. The animals 
give off certain nitrogenous wastes which are used in the manu- 
facture of protein within the plant. The animals eat the plants 
and give off organic waste, which the plants use as food and 
make into living matter. When the plants give off as much 
oxygen as the animals use and the animals give off as much 
carbon dioxide as the plants use, the aquarium is balanced. 

Relations between Green Plants and Animals. — What goes 
on in the aquarium is an example of the relation existing between 



Carbon dioxide 
(CO2) 



Water 
VHgO) 



Carbon dioxide 
n (CO2) 



Simple Salts 



Water 
'CHaO) 



(NH3) 



Plants 

with chlorophyll 

buildup complex 

organic substances 

They store up 

energy from the sun 

in the process 

and 



Animals 
and plants without 
/ chlorophyll 

I . (which tear down complex! Ammonia 

organic > 

'food of \ organic substances ] (NHg) 

and set free energy 

in the process iii 

form of heat 



/ t ^ 

Energy from sum 



/ \ \ 

Energy set free 

as heat. 

The relations between green plants and animals 



all green plants and all animals. Everywhere in the world green 
plants are making food which becomes, sooner or later, the food 
of animals. Man may not feed upon the leaves of plants, but 
he eats fruits and seeds in one form or another. Even if he 
does not feed directly upon plants, he eats the flesh of herbivo- 
rous animals, which in turn feed directly upon plants. And so 
it is the world over; the plants are the food-makers and supply 
the animals. Green plants also give a very considerable amount 
of oxygen to the atmosphere every day, which the animals may 
make use of. 

The Nitrogen Cycle. — The animals in their turn supply 
much of the carbon dioxide that the plant uses in starch- 
Dlaking. They also supply most of the nitrogenous matter used 



168 THE RELATIONS' OF PLANTS TO ANIMALS 



.^e^*^ 



etc 



Animal Life 

ng Bacteria^, 




Soil) 



Nitrites 
"^ Nitric Bacteria 

The nitrogen cycle. 



by the plants, whether from the decay of dead bodies or the 
excretions of the Hving. Bacteria which hve upon the roots of 
certain plants, are the only organisms that can take nitrogen 
from the air. Thus, in spite of all the nitrogen of the at- 
mosphere, plants and 
animals are limited in 
the amount available. 
And the available supply 
is used over and over 
again, perhaps in nitrog- 

Bacteria/ ^^t^'*' enous food by an animal, 

V^^ ^f'^^k^ then it may be given off 

as organic waste, get into 
the soil, and be taken up 
by a plant through the 
roots. Eventually the nitrogen forms part of the food supply 
in the body of the plant, and then may become part of its 
living matter. When the plant dies, the nitrogen is returned 
to the soil. Thus the 
usable nitrogen is 
kept in circulation. 

Symbiosis. — Plants 
and animals are seen 
in a general way to 
be of mutual advan- 
tage to each other. 
Some plants, called 
lichens, show this 
mutual partnership in 
the following interest- 
ing way. A lichen is 
composed of two 
kinds of plants, one 
of which at least may 

live alone, but the two plants have formed a partnership for life, 
and have divided the duties of such life between them. In most 
lichens the alga, a green plant, forms starch and nourishes the 
fungus. The fungus, in turn, produces spores, by means of which 




A lichen (Physcia stellaris). Photographed by 
W. C. Barbour. 




A HAY INFUSION 169 

new lichens are started in life; moreover, the Hchen is usually 
protected by the fungus, which is stronger in structure than the 
green part of the combination. This process of living together for 
mutual advantage is called sijmhio'sis. Some animals also combine 
with plants; for example, the tiny animal known as the hydra 
with certain of the one-celled algse, 
and, if we accept the term in a 
wide sense, all green plants and 
animals live in this relation of 

, . 1 J 1 A • 1 Stages in the formation of 

mutual give and take. ^ Annnals the lichen thaiius, showing the 
also frequently live in this relation relation of the threadlike 

, ^ J.^ j.T„ x* I, I,* u fungus to the green cells of 

to each other, as the tmy crab which ^^^ ^^^^^ ^^^/r Bornet.) 
lives within the shell of the oyster; 

and the sea anemones which are carried around on the backs of 
some hermit crabs, aiding the crab in protecting it from its 
enemies, and being carried about by the' crab to places where 
food is plentiful. 

A Hay Infusion. — Still another example of the close relation 
between plants and animals may be seen in the study of a hay 
infusion. If we place a wisp of hay or straw in a small glass 
jar nearly full of water, and leave it for a few days in a warm 
room, certain changes are seen to take place in the contents of 
the jar; the water after a little while gets cloudy and darker 
in color, and a scum appears on the surface. If some of this 
scum is examined under the compound microscope, it will be 
found to consist almost entirely of bacteria. These bacteria 
evidently aid in the decay which (as the unpleasant odor from 
the jar testifies) is iaking place. As we have learned, bacteria 
flourish wherever the food supply is abundant. The water 
within the jar has come to contain much of the food material 
which was once within the leaves of the grass, — organic nutri- 
ents, starch, sugar, and proteins, formed in the leaf by the 
action of the sun on the chlorophyll of the leaf, and now released 
into the water by the breaking down of the walls of the cells. 
The bacteria themselves release this food from the hay by 
causing it to decay. After a few days small one-celled animals 
appear which multiply with wonderful rapidity. Hay is dried 
grass, upon which the wind may have scattered some of these 

HUNT. NEW ES. — 12 



170 THE RELATIONS OF PLANTS TO ANIMALS 

little organisms in the dust from a dried-up pool. Existing in 
a dormant state on the hay, they are awakened by the water 
to active Ufe. In the water, too, there may have been some 
living cells, plant and animal. 

At first the multiplication of the tiny animals within the hay 
infusion is extremely rapid; there is food in abundance and near 
at hand. After a few days more, however, several kinds of 




Life in a late stage of a hay infusion. B, bacteria, swimming 
or forming masses of food upon which the one-celled animals, 
the paiamecia, are feeding; G, gullet; F.V., food vacuole; 
C.V., contractile vacuole; P, pleurococcus; P.D., pleurococcus 
dividing. Highly magnified. 

one-celled animals may appear, some of which prey upon others. 
Consequently a struggle for life begins, which becomes more 
and more intense as the food from the hay is used up. Eventu- 
ally the end comes for all the animals unless some green plants 
obtain a foothold within the jar. If such a thing happens, 
food will be manufactured within their bodies, a new food 
supply arises for the animals within the jar, and a balance of 
life results. 



THE RELATIONS OF PLANTS TO ANIMALS 171 

Summary. — This chapter shows us that there exists a give 
and take relationship between green plants and animals which is 
illustrated by the condition known as symbiosis. 

Problem question. — 1. How does the balanced aquarium illus- 
trate symbiosis? 

2. Explain the nitrogen cycle, the carbon cycle, the oxygen 
cycle. 

3. What kind of a relationship does life within a hay infusion 
represent? 

Problem and Project References 

Eggerling and Ehrenberg, The Fresh Water Aquarium and its Inhabitants. Henry 

Holt and Company. 
Furneaux, Life in Ponds and Streams. Longmans, Green and Company. 
Hunter, Laboratory Problems in Civic Biology. American Book Company. 
Parker, Lessons in Elementary Biology. The Macmillan Company. 
Sedgwick and Wilson, General Biology. Henry Holt and Company. 
Sharpe, A Laboratory Manual. American Book Company. 



XV. THE PROTOZOA 

Problem, The study oj a one-celled animal. (Laboratory 
Ma7iual, Problem X XV; Laboratory Problems, Probs, 112, 113.) 

(a) In its relation to its surroundings. 

(b) As a cell. (Optional.) 

(c) In its relations to man, 

A Simple Plant Cell. — We have seen that perhaps the 
simplest plant would be exemplified by one of the tiny bacteria 
we have just read about. A typical one-celled plant, however, 
would contain green coloring matter or chlorophyll, and would 
have the power to manufacture its own food under conditions 
giving it a moderate temperature, a supply of water, oxygen, 
carbon dioxide, and sunlight. Such a simple plant is the pleu- 
rococcus, the " green slime " seen on the shady side of trees, 
stones, or city houses. This plant would meet our definition 
of a cell, as it is a minute mass of protoplasm inclosed in a 
cell membrane and containing a nucleus. It is surrounded by a 
walP of a woody material which covers the delicate membrane 
formed by the activity of the protoplasm within the cell. It 
also contains green granules called chloroplasts. Of their part in 
the manufacture of organic food we have already learned. Such 
is a simple plant cell. Let us now examine a simple animal cell 
in order to compare it with that of a plant. 

The Paramecium. — The one-celled animal most frequently 
found in hay infusions is the Paramecium (par-a-me'shi-um), or 
slipper animalcule (so-called because of its shape). 

This cell is elongated, oval, or elliptical in outline, but some- 
what flattened. Seen under the low power of the microscope, 
it appears to be extremely active, rushing about now rapidly, 
now more slowly, but seemingly always taking a definite course. 

^ This shows one practical reason why plant food often contains more indi- 
gestible matter thaq aniw^'l food of same bulk. 

172 



PARAMECIUM 



173 



The rounded end of the body (the anterior end) usually goes 
first. If it pushes its way between dense substances in the 
water, the cell body is seen to change its shape as it squeezes 
through. 

The cell body is almost transparent, and consists of semifluid 
protoplasm which has a granular, grayish appearance under the 
microscope. This protoplasm appears to be 
bounded by a very delicate membrane (the 
cu'ticle) through which project numerous 
delicate threads of protoplasm called cilia CV^ 
(sil'i-a). (These are seen with difficulty 
under the microscope.) 

The locomotion of the Paramecium is 
caused by the movement of these cilia, 
which lash the water like a multitude of 
tiny oars. The current of water caused by 
the cilia carries tiny particles of food into a 
funnel-like opening, the gullet, on one side of 
the cell. Once within the cell body, the V- 
particles of food materials are gathered into 
little balls within the almost transparent 
protoplasm. Each mass of food seems to 
be inclosed within a little area containing 
fluid, called a vacuole (vak'u-ol). Other 
vacuoles appear to be clear; these are spaces ^^' contractile vacuole; 
in which food has been digested. One or mouth; G, gullet- M, 
two larger vacuoles may be found; these are macronucieus;Mi,micro- 

- „ ^ - . nucleus; V, vacuole. 

the contractile vacuoles; their purpose seems 
to be to pass off waste material from the cell body. This is 
done by the pulsation of the vacuole, which ultimately bursts, pass- 
ing fluid waste to the outside. Solid wastes are passed out of 
the cell in somewhat the same manner. The nucleus of the cell 
is not easily visible in living specimens. In a cell that has been 
stained it has been found to be a double structure, consisting of 
one large and one small portion, called respectively the macro- 
nucleus and the micronucleus. 

Response to Stimuli. — In the Paramecium, as in the one- 
celled plants, the protoplasm composing the cell can do certain 




Paramecium: C, cilia; 



174 



THE PROTOZOA 



things. Protoplasm responds, in both plants and animals, to 
certain agencies acting upon it, coming from without; these 
agencies we call stimuli. Such stimuli may be light, differences 
of temperatm^e, presence of food, electricity, or other factors in 
its surroundings. Plant and animal cells may react differently 
to the same stimuli. In general, how^ever, we know that pro- 
toplasm is irritable to some of these factors. To severe stimuli, 
protoplasm usually responds by contracting, another power which 
it possesses. We know, too, that plant and animal cells take in 
food and change the food to protoplasm, that is, that they as- 
similate food; and that they may waste away and repair them- 
selves. Finally, we know that new plant and animal cells are 
reproduced from the original bit of protoplasm, a single cell. 

Reproduction of Paramecium. — Sometimes a Paramecium 
may be found in the act of dividing by the process known as 

fission^ to form two new cells, each of which 

contains half of the original cell. In this 

process the nucleus first elongates and breaks 

into two, and the halves go 

to opposite ends of the cell. 

The cell elongates, a second 

gullet appears, and ulti- 
M mately the cell -breaks into 

two parts, each haff pro- avl 

vided with a nucleus and a 

gullet (see diagram). This Paramecium, high- 

_ Paramecmmdivid- -^ ^ method of aSCXUal re- ly magnified; two 
mg by fission High- ^eUs just before con- 

ly magnified. M, production. jugation. M, mouth; 

ZTucieZ^%Tc' Frequently another stage MW micronucieus; 

cronucieus, mi^., i ,. i t_ il/AC.,macionucleus; 

tmcronucleus. (After 01 reproduction may be Ob- ^y contractile vac- 

Sedg^ick and WU- ^^j^^^^ ^his is Called con- uole'.' (After Sedgwick 

^^•> • s' J I, ^ andWHson.) 

jugation, and somewhat re- 
sembles conjugation in the simple plants. Two cells of 
equal size attach themselves together as shown in the Figm-e. 
Complicated changes take place in the nuclei of the two cells 
thus united, which results in an exchange of parts of the mate- 
rial forming the nuclei of each celL After a short period 
of rest the two cells separate. The stage of conjugation we 



MAC. 
MIC. 





IM!C. 
MAC. 



AMCEBA 175 

believe in the plants to be a sexual stage. There seems every 
reason to believe that it is a like stage in the life history of the 
Paramecium. 

Amoeba.^ — In order to understand more fully the life of a 
simple bit of protoplasm, let us take up the study of the 
amoe'ba, a type of the simplest form of life known, either plant 
or animal. Unlike the plant and animal cells we have examined, 
the amoeba has no fixed form. r;-,.^ 
Viewed under the compound P'^gjj'j^^^ 
microscope, it has the appear- )^^^§fSl^ 



ance of an irregular mass of "wKKi- 

granular protoplasm. Its form 

is constantly changing as it 

moves about. This is due to ^— %I^^SIf ^•■:0:: -.- ■:"-^ 

the pushing out of tiny pro- ^,||p:;^;{i^^o- :S:.;:S^-;:'; '-J-'-v'-'^lgP'^ 

jections of the protoplasm of Ecj:^^^^^^^^-^^^ 
the cell, called pseudopodia ^BM 



(su-do-po'di-a; false feet). ^"^i^Pl^^P^-""*^ 
The outer layer of protoplasm '-^$A^_JS^^0^""^ 
is not so granular as the inner • i^iyt^^"'-'^ 

part; this outer layer is called 

ec'toplasm, the inside being An amoeba in search ot food. P pseu- 

^ /7 7 T 1 clopodium; F, food vacuole ; £;c, ectoplasm; 

called en doplasm. In the En, endoplasm; C, contractile vacuole; 

central part of the cell is the ^' nucleus. 

nucleus. Several theories have been advanced to account for 
locomotion. The most likely one seems to be that the pseudo- 
podia are elastic and when stretched out fasten themselves. 
The rest of the body then flows into the extended end. Some 
writers think the amoeba progresses by a kind of rolling motion. 
The pseudopodia are pushed out in the direction in which the 
animal is to go, the rest of the body following. 

Although but a single cell, still the amoeba appears to be aware 
of the existence of food when it is near at hand. Food may 
be taken into the body at any point, the semifluid protoplasm 

1 Amoeb£B may be obtained from the hay infusion, from the dead leaves in 
the bottom of small pools, from the same source in fresh-water aquaria, from 
the roots of duckweed or other small water plants, or from green algae growing 
in quiet localities. No sure method of obtaining them can be given. 



176 



THE PROTOZOA 



/ 2 



4 

. Mi 



/f - V 



simply roiling over and engulfing the food material. Within the 
body, as in the Paramecium, the food is inclosed within a fluid 
space or vacuole. The protoplasm has the power to take out 
such material as it can use to form new protoplasm or to give 
energy. It will then rid itself of any material that it cannot 
use. Thus it has the power of selective absorption, sl property 
found in the protoplasm of plants previously studied. Circu- 
lation of food material is accomplished by the constant streaming 

of the protoplasm within the 
cell. The cell absorbs oxygen 
from the air in the water by 
osmosis through its delicate 
membrane, giving out carbon 
dioxide in return. Thus res- 
piration takes place through 
every part of the covering of 
the cell. Waste products 
other than carbon dioxide 
formed from the life activi- 
ties which take place within 
the cell are passed out by 
means of the contractile vac- 
uole. 

The amoeba, like other one- 
celled organisms, reproduces 
by the process of fission. A 
single cell divides by splitting 
into two, each of which re- 
sembles the parent cell, except 
that it is of smaller size. 
When these new cells become 
the size of the parent amoeba, they each divide. This is a kind 
of asexual reproduction. When conditions unfavorable for life 
come, the amoeba, like some one-celled plants, encysts itself 
within a membranous wall. In this condition it becomes dried 
and is blown through the air. Upon return to a favorable 
environment, the cover disappears and life begins again, as be- 
fore. In this respect the amoeba resembles the spore of a plant. 






6 



Amoeba, highly magnified, showing the 
changes which talce place during division. 
The dark body in each Figure is the 
nucleus; the transparent circle, the con- 
tractile vacuole; the outer, clear portion 
of the body, the ectoplasm; the graniilar 
portion, the endoplasm; the granular 
masses, food vacuoles. 



AMCEBA 



177 



From the study of the amoebalike organisms which are known to cause 
malaria, and by comparison with the amoebae which live in ponds and swamps, 
it seems likely that every amoeba has a complicated life history during 
which it passes through a sexual stage of existence. 

The Cell as a Unit. — - In the daily life of a one-celled animal 
we find the single cell performing all the vital activities which 
we shall later find that the many-celled animal is able to perform. 
In the amoeba no definite parts of the cell appear to be set off 
to perform certain functions; but any 
part of the cell can take in food, can 
absorb oxygen, can change the food 
into protoplasm and excrete the waste 
material. The single cell is, in fact, 
an organism able to carry on the 
business of living as effectually as a 
very complex animal. 

Complex One-celled Animals. — In the 

Paramecium we fiijd a single cell but certain 
parts of the cell have certain definite func- 
tions: the cilia are used for locomotion; a 
definite part of the cell takes in food, while 
another definite spot passes out the waste. 
In another one-celled animal called vorti- 
cel'la, part of the cell has become very much 
elongated and is contractile, forming a stalk 
by which the Uttle animal is fastened to a 
water plant or other object. The stalk may 
be said to act like a muscle fiber, as its sole 
function seems to be movement; the cilia 
are located at one end of the cell and serve 
to create a current of water which brings 
food particles to the mouth. Here we have 
several parts of the cell each doing a differ- 
ent kind of work. This is known as physi- 
ological division of labor. 

Habitat of Protozoa. — Protozo'a, or one-celled animals, are 
found in shallow water almost everywhere, seemingly never at 
any great depth. They appear to be attracted to the surface 
by light and the supply of oxygen. Every fresh-water lake 
swarms with them; the ocean contains countless myriads of 
many different forms. 















MOUTH OPMNim 


XCILIA 


: --'^m^^ — ^ 


CUTICLE ■ 

1 




i 




STALK OR 
PEDICLE 




i-.....;. :... 


CONTRACTILE 


* BASAL 
ATTACHMENT 


i 

■■■■■■'«■<■.;.... . ■ ■■ ■ ■■■■-»'«*v*. 





Vorticella, highly magnified. 
Photograph from American 
Museum of Natural History. 



178 



THE PROTOZOA 



Use as Food. — Protozoa are so numerous in lakes, rivers, and 
the ocean as to form the food for many animals higher in the 
scale of life. Almost all fish that do not take the hook and that 
travel in schools, or companies, migrating from one place to 
another, live partly on such food. Alany feed on slightly larger 
animals, which in tm-n eat the Protozoa. Such fish have on 
each side of the mouth attached to the gills a series of small 
structures looking like tiny rakes. These are called the gill 
rakers, and aid in collecting tiny organisms from the water as 
it passes over the gills. 

Relation of Protozoa to Disease. — The study of the life his- 
tory and habits of the Protozoa has resulted in the finding of 

many parasitic forms, 
-f ^ ^ and the consequent ex- 
"^ ' planation of some kinds 
of disease. One parasitic 
protozoan like the amoeba 
causes the disease known 
as malaria. Part of its 
life is passed within the 
body of a mosquito, — the 
anopheles (a-nof'e-lez), 
— into the stomach of 
which it passes when 
the mosquito sucks 
blood from a person 
having malaria. Within 
the body of the mosquito 
a complicated part of 
the life history takes 
place, which results in a 
stage of the parasite 
establishing itself within 
the glands which secrete 
the saliva of the mos- 




(3 "^^*'^^*~ ^''^ ®^/ 



Life history of tiie malarial parasite. The 
mosquito injects crescent-shaped bodies A into 
the blood of man. Spores develop in the blood 
corpuscles, and many, as at H, may enter other 
corpuscles, while some (P) may be drawn into the 
body of a mosquito, where the parasite passes 
through sexual stages. Follow the course shown 
by the arrows from A back to A, and from H back 
toH. 



quito. When the mosquito pierces its human prey the next 
time, some of the parasites are introduced with the saliva 
into the victim's blood. These parasites enter the red corpuscles 



RELATION OF PROTOZOA TO DISEASE 179 

of the blood, increase in size, and then form spores. The rapid 
process of spore formation results in the bursting of the blood 
corpuscles, and the parasites enter the fluid portion of the blood. 
The chill and fever are probably caused by the destruction of the 
corpuscles and release of poison into the blood. The parasites 
again enter the blood corpuscles and in forty-eight or seventy-two 
hours repeat the process thus described. Yellow fever is un- 
doubtedly conveyed by another species of mosquito, and is due 
to the presence of a protozoan similar to that of malaria in the 
blood. That these diseases may be stamped out by the exter- 
mination of the mosquitoes, which may be accomplished by 
the use of oil to prevent their breeding in swamps, by draining 
the swamps, or by the introduction of fish which eat the mos- 
quito larvse, has been proved from our experience along the 
Panama Canal, in the Philippines, in Cuba, and in New Orleans. 

Many other diseases of man are probably caused by parasitic 
protozoans. Dysentery appears to be caused by the presence 
of an amoebalike animal in the digestive tract. Smallpox, 
rabies, and possibly other diseases may be caused by the action 
of these little animals. 

Another group of protozoan parasites are called trypanosomes 
(trip'a-no-somz). One of this family lives in the blood of native 
African zebras and antelopes; seemingly it does them no harm. 
But if one of these parasites is transferred by the dreaded tsetse 
(tset'se) fly to one of the domesticated horses or cattle of the 
colonists in Central or Southern Africa, death of the animal 
results. 

Another fly carries a specimen of trypanosome to the natives 
of Central Africa, which causes ^' the dreaded and incurable 
sleeping sickness." This disease has carried off more than fifty 
thousand natives in a year, and many Europeans have suc- 
cumbed to it. Its ravages are now largely confined to an area 
near the large Central African lakes and the upper Nile, for 
the fly which carries the disease fives near water, seldom going 
more than 150 feet from the banks of streams or lakes. The 
British government is now trying to control the disease in 
Uganda by moving all the villages at least two miles from the 
lakes and rivers. Why? In this country many fatal diseases 



180 



THE PROTOZOA 



of cattle, as '' tick," or Texas fever, are probably caused by 
protozoans. 

Skeleton Building. — Some of the Protozoa build elaborate skeletons. 
These may be formed either in or outside of the body, and are often of 

great beauty when seen under the mi- 
croscope (see Figure). Much of the chalk 
in various parts of the world is made 
of the skeletons of these tiny creatures. 

A Simple Classification of Protozoa 

The following are the principal classes 
of Protozoa, examples of which we have 
seen or read about: — 
Class I. Rh'.zip' oda (Greek — root- 
footed). Having no fixed form; 
with pseudopodia. Either naked 
as Amoeba or building lim^' {For- 
aminif'era) or glasslike skeletons 
(Radiola'ria) . 
Class II. Infusoria (infusions). Usually 
active ciliated Protozoa. Examples, 
Paramecium, Vorticella. 
Class III. Sporozo'a (spore animals). Usually parasitic and nonactive. 
Example, the parasite that causes malaria (Plf,smodium malaria'). 

Summary. — This study has shown us that a single-celled 
animal has all the vital functions of a more complex one. It 
feeds, digests, and assimilates its food, breathes, excretes waste, 
and reproduces. It is sensitive to outside stimuli and responds 
by movement. It is in other words a living organism. 

Problem Questions. — 1. Describe the life cycle of a Para- 
mecium. 

2. Compare two stages of reproduction in Paramecium. 

3. What relation do the Protozoa bear to malaria? Explain. 




Skeleton of a radiolarian. Highly 
magnified. From model at Amer- 
can Museum of Natural Historj\ 



Problem and Project References 

Calkins, Biology. Henry Holt and Company. 

Calkins, The Protozoa. Lemoke. 

Hegner, Introduction to Zoology. The Macmillan Company. 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Sedgwick and Wilson, General Biology. Henry Holt and Company. 

Sharps, A Laboratory Manual. American Book Company. 



XVI. SIMPLE METAZOA — DIVISION OF LABOR 

Problem, An introductory study of many-celled animals to 
learn something about — 

(a) Their development. 

(b) The structure of a sponge. 

(c) The hydra, 

(d) The development of tissues and organs, 

(e) The common functions of all animals, 

(Laboratory Manual, Prob. XXVI; Laboratory Problems, 
Probs. 116, 117.) 

Reproduction in Plants. — Although there are very many 
plants and animals so small and so simple as to be composed 
of but a single cell, by far the greater part of the animal and 
plant world is made up of individuals which are collections of 
cells living together. 

In a simple plant like the pond scum, a string or filament of 
cells is formed by a single cell dividing crosswise, each of the 
two cells thus formed giving rise to two more, and so on, until 
eventually a long thread of cells results. Such growth of cells 
is asexual. 

In some instances, however, a single cell is formed by' the 
union of two cells, one from each of the adjoining filaments of 
the plant. Around this cell eventually a hard coat is formed, 
and the spore, as it is called, is thus protected from unfa- 
vorable changes in the surroundings. Later, when conditions 
become favorable for its germination, the spore may form a 
new filament of pond scum. 

In the seed plants, too, we found within the seed a little 
plant, an embryo, which, under favorable conditions, may give 
rise, through the rapid multiplication of the cells forming it, to 
a new plant. The embryo first arises from two cells, one of 
which, called a sperm, comes from a pollen grain, while the 
other, the egg, is found within the embryo sac of the ovary. 

181 



182 sumple metazoa — division of labor 

Reproduction in Animals. — Similarly, in the reproduction of 
many-celled animals the new individual is formed by the union 
of a sperm and an egg cell. A common bath sponge, an earth- 
worm, a fish, and a dog, — each and all of them begin life in 
precisely the same way. Animals which are thus composed of 
many cells are known as the Metazo'a, as distinguished from the 
Protozoa, which are made of but a single cell. 

Sexual Development of a Simple Animal. — In a man3'-celled 
animal the life history begins with a single cell, the fertilized 
egg. This c^ll, as we remember, has been formed b}^ the union 
of two other cells, a tiny (usuall}^ motile) cell, the sperm, and 
a large cell, the egg. After the egg is fertilized by a sperm cell, 
it splits into two, then into four, then into eight, then into six- 
teen cells, and so on; as the number of cells increases, a hol- 
low baU of cells called the bias' tula is formed; later this ball 








O 

Stages in the segmentation of an egg, showing the formation of the gastrula. 

sinks in on one side, and a double-walled cup of cells, called 
a gas'trula, results. Practicalh^ all animals pass through the 
above stages in their development from the egg, although these 
stages are often not easy to see because of the presence of food 
material (yolk) in the egg. In the development of the sponge 
the gastrula, which swdms by means of cilia, soon settles down, a 
skeleton is formed, other changes take place, and the sponge begins 
life as an animal attached to some support in the water. The 
early stages of life, when an animal is unlike the adult, are known 
as larval stages; the animal at this time being called a larva. 

The young sponge consists of three layei-s of cells: those of 
the outside, developed from the outer layer of the gastrula, are 
called ec'toderm; the inner laj^er, developed from the inner 
layer of the gastrula, the en'doderm; and the middle, almost 
structureless layer, the mes'oderm. In higher animals the 
mesoderm gives rise to muscles and parts of other internal 
structures. 



THE SPONGE 



183 




A horny fiber sponge; IP, the incurrent 
pores; O, osculum. Notice that this sponge 
is made up of apparently several individuals. 
One fourth natural size. 



The Structure of a Sponge. — The simplest kind of sponge 
has the form of an urn, attached at the lower end. A com- 
mon sponge living in Long Island Sound is a tiny urn-shaped 
animal less than an inch 
in length. It has a 
skeleton made up of very 
tiny spicules of lime, of 
different shapes. Cut 
lengthwise, such an 
animal is seen to be 
hollow, its body wall 
pierced with many tiny 
pores or holes. The 
bath sponge, the skeleton 
of which is made up of 
fibers of horn, or a 
variety known as the 
finger sponge, shows the 

pores even better than the smaller limy sponge. In a bath sponge, 
however, we probably have a colony of sponges living together. 

Each sponge has a large number of 
pores opening into a central cavity, 
which in turn opens by a large hole, 
called the os'culum, to the surround- 
ing water. 

A microscopic examination shows 
the pores of the sponge to be Uned 
on the inside with cells each having a 
collar of living matter surrounding a 
single long cilium called a flagellum 
(fla-jerum). The flagella, lashing in 
one direction, set up a current of 
water toward the large inner cavity. 
This current bears food particles, 
tiny plants and animals, which are 
seized and digested by the collared cells, these cells probably 
passing the food on to the other cells of the body. The jelly- 
like middle layer of the body is composed of cells which secrete 




Longitudinal section of a 
simple sponge: O, osculum, 
P, P, incurrent pore; /, 
flagella. 



184 SIMPLE METAZOA — DIVISION OF LABOR 



Castrula 




Tentdcle — 
Stinging Cell- 
young Sperm- 
Producing Organ. 

Digestive Caviiy ^ 

Mature egg- 
Blast ul a- - 



Mature Sperm- 
Reducing Organ 

~ Mouth 
^ Tentacle 



Young egg 

y. Basal disk 

Longitudiual section of a hydra, magnified. 



lime to form the spicules and the reproductive cells, eggs, and 
sperms. 

The Hydra. — Another very simple animal, which unlike most 
sponges Uves in fresh water, ^ is called the hydra. This little 
creature is shaped like a hollow cyhnder with a cu'cle of arms 

or ten'tades at the free end. 
It is found attached to dead 
leaves, sticks, stones, or water 
weeds in most fresh-water 
ponds. When disturbed, the 
hydra contracts into a tiny 
whitish ball a little larger than 
the head of a pin. Expanded, 
it may stretch its tentacles in 
search of food almost an inch 
from their point of attach- 
ment. The tentacles are pro- 
vided with batteries of minute 
darts of stinging cells, by means of which prey is caught and 
killed. The outer layer of the animal serves for protection as 
well as movement and sensation, certain cells being fitted for 
each of those different pm-poses. 

Food Taking. — The tentacles then reach out Hke arms, grasp 
the food, bend over ^dth it, and pull it toward the mouth. Cer- 
tain cells lining the hollow digestive ca\aty pour out a fluid 
which digests the food. Other cells with long cilia circulate the 
food, while still other cells hning the cavity put out pseudo- 
podia, which grasp and ingest the food particles. The tentacles 
are hollow, and the digestive cavity extends into them. The 
outer layer of the animal does not digest the food, but receives 
some of it already digested from the inner layer. This food 
passes from cell to cell, as in plants, by osmosis. The oxj^gen 
necessary to oxidize the food is passed through the body wall, 
seemingly at any point, for there are no special organs for 
respiration. 

Reproduction. — The hydra reproduces itself either by budding 
asexually or by means of eggs and sperms, sexually. The bud ap* 

* A few Bponges, for example, spongUla, live in fresh water. 



DIVISION OF LABOR 185 

pears on the body as a little knob, sometimes more than one 
coming out on the hydra at the same time. At first the bud is 
part of the parent animal, the body cavity extending into it. 
After a short time (usually a few days) the young hydra sepa- 
rates from the old one and begins life alone. This is asexual 
reproduction. 

The hydra also reproduces by eggs and sperms. These sperms 
are collected in little groups which usually appear near the free 
end of the animal, the egg cells developing near the base of the 
same hydra. Both eggs and sperms grow from the outer layer 
of the animal. The sperms, when ripe, are set free in the water; 
one of them unites with an egg, which is usually still attached 
to the body of the hydra, and development begins which results 
in the growth of a new hydra in a new locality. 

The stages passed through in development resemble closely 
those described on page 182, and it would not be hard to 
imagine the gastrula stage, turned upside down with a circle of 
tentacles at the open end. Our gastrula would then be a hydra. 

Division of Labor. — If we compare the amoeba and the Para- 
mecium, we find the latter a more complex organism than the 
former. An amqpba may take in food through any part of the 
body; the Paramecium has a definite gullet. The amoeba may 
use any part of the body for locomotion; the Paramecium has 
definite parts of the cell, the ciHa, fitted for this work. Since 
the structure of the Paramecium is more complex, we say that 
it is a '^ higher " animal. In the vorticella, a still more complex 
organism, part of the cell has grown out like a stalk, has become 
contractile, and acts and looks like muscle. 

As we look higher in the scale of life, we invariably find that 
certain parts of a plant or an animal are set apart to do certain 
work, and only that work. Just as in a community of people, 
there are some men who do rough manual work, others who are 
skilled workmen, some who are shopkeepers, and still others 
who are professional men, so amoiig plants and animals, where- 
ever collections of cells live together to form an organism, there 
is division of labor, some cells being fitted to do one kind of 
work, while others are fitted to do work of another sort. 

AS we have seen in plants, this results in a large number of 

FTINT. NEW US. — 13 



186 SIMPLE METAZOA — DIVISION OF LABOR 

collections of cells in the body, the cells in each collection being 
alike in structure and in performing the same function. Such 
a collection of cells we call a tissue. (See Chapter III.) 

Frequently several tissues have certain functions to perform 
in conjunction with one another. The arm of the human body 
performs movement. To do this, several tissues, as muscles, 
nerves, and bones, must act together. A collection of tissues 
which work together to perform one function is called an organ. 

In the sponge, division of labor occurs between the cells of 
a simple animal, some cells lining the incurrent pores creating 
a current of water, and feeding upon the minute organisms 
which come within reach, other cells building the skeleton of 
the sponge, still others producing eggs or sperms. Division of 
labor of a more complicated sort is seen in the hydra. Here 
the cells which do the same kind of work are collected into 
tissues, each tissue being a collection of cells, all of which are 
more or less alike and do the same kind of work. But in higher 
animals which are more complicated in structure and in which 
the tissues are found working together to form organs, division 
of labor is still more developed. In the human arm, an organ 
fitted for certain movements, think of the number of tissues 
and the complicated actions which are possible. The most 
extreme division of labor is seen in the organism which has the 
most complex actions to perform and whose organs are fitted 
for such work. 

In our daily life in a town or city we see division of labor 
between individuals. Such division of labor may occur among 
other animals, as, for example, bees or ants. But it is seen 
at its highest in a great city or in a large business or industry. 
In the stockyards of Chicago, division of labor has resulted in 
certain men performing but a single movement during their 
entire day's work, but this movement repeated so many times 
in a day has resulted in wonderful accuracy and increased speed. 
Thus division of labor attains its end. 

Tissues in the Human Body. — Every animal body above the 
protozoan is composed of a certain number of tissues. The cells 
making up these tissues have certain well-defined characteris- 
tics. In very simple animals the cells are all very much alike 



TISSUES IN THE HUMAN BODY 



187 



but in more complex animals the cells are more and more unlike 
as their work becomes more and more different. Let us see 
what these cells may be, what their structure is, and, in a general 
way, what function each has in the human body. 

Muscle Cells. — A large part of our body is made up of 
muscle. Muscle cells are elongated in shape, and have great 
contractile power. Their work is that of causing movement, 
and this is usually done by means of attachment to a skeleton 
inside the body. In man they may be of two kinds, voluntary 
(under control of the will) and involuntary. 

Epithelial Cells cover the outside of a body or line the inside 
of the cavities in the body. The shape of these cells varie? 




Diagrams of sections of cells, greatly magnified, e, flat cell (epithelium) 
from mouth; c, columnar epithelium from food tube; 6, bone-forming cell; 
I, liver cell; m, muscle cell; /, fat cell; n, nerve cell. 



from flat plates to little cubes or columns depending upon their 
position in the body. Some bear cilia, an adaptation. Can 
you think of their purpose? 

Connective Tissue Cells form the framework between tissues 
in the body. They are characterized by possessing numerous 
long processes. Around them is found to a greater or less 
degree a structureless material, called intercellular substance. 
This stands in the same relation to the cells as does mortar to 
the bricks in a wall. 

Several other types of cells might be mentioned, as blood 
cells, cartilage cells, bone cells, and nerve cells. A glance at the 
Figure shows their great variety of shapes and sizes. 



188 SIMPLE METAZOA — DIVISION OF LABOR 

Functions Common to All Animals. — The same general func- 
tions performed by a single cell are performed by a many-celled 
animal. But in the Metazoa the various functions of the single 
cell are taken up by the organs. In a complex organism, like 
man, the organs and the functions they perform may be briefly 
given as follows : — '- 

(1) The organs of food taking. Food may be taken in by 
individual cells, as those lining the pores of the sponge, or definite 
parts of a food tube may be set apart for this purpose, as the 
mouth and parts which place food in the mouth. 

(2) The organs of digestion: the food tube and collections of 
cells which form the glands connected with it. The enzymes in 
the fluids secreted by the latter change the foods from a solid 
form (usually insoluble) to that of a liquid. Such liquid may 
then pass by osmosis through the walls of the food tube into 
the blood. 

(3) The organs of circulation: the tubes through which the 
blood, bearing its foods and oxygen, reaches che tissues of the 
body. In simple forms of Metazoa, as the sponge and hydra, 
no such organs are needed, the fluid food passing from cell to 
cell by osmosis. 

(4) The organs of respiration: the organs in which the blood 
receives oxygen and gives up carbon dioxide. The outer layer 
of the body serves this purpose in very simple animals; gills 
or lungs are developed in more complex animals. 

(5) The organs of excretion: such as the kidneys and skin, 
which pass off nitrogenous and other waste matters from the 
body. 

(6) The organs of locomotion: muscles and their attachments 
and connections; namely, tendons, ligaments, and bones. 

(7) The organs of nervous control: the central nervous system, 
which has control of coordinated movement. This consists of 
scattered cells in low forms of life; such cells are collected into 
groups and connected with each other in higher animals. 

(8) The sense organs: collections of cells having to do with 
sight, hearing, smell, taste, and touch. 

(9) The orgaRS of reproduction: the sperm and egg forming 
glands. 



SPONGES, CCELENTERATES 



189 



Almost all animals have the functions mentioned above. In 
most, the various organs mentioned are more or less developed, 
although in the simpler forms of animal life some of the organs 
mentioned above are either very poorly developed or entirely 
lacking. 

Forms of Simple Metazoans. Sponges ^ 

Sponges (Porifera) may be placed, according to the kind of skeleton 
they possess, in the following groups: — 

(1) The limy sponges, in which the skeleton 
is composed of spicules of carbonate of lime. 
Grantia is an example. 

(2) The glassy sponges. Here the skeleton 
is made of silica or glass. Some of the rarest 
and most beautiful of all sponges belong in 
this class. The Venus's flower basket is an 
example. 

(3) The horny fiber sponges. These, the 
sponges of commerce, have the skeleton com- 
posed of tough fibers of material somewhat 
like that of cow's horn. This fiber is elastic 
and has the power to absorb water. In a liv- 
ing state, the horny fiber sponge is a dark- 
colored fleshy mass, usually found attached to 
rocks. The warm waters of the Mediterranean 
Sea and the West Indies furnish most of our 
sponges. The sponges are pulled up from their 
resting places on the bottom, by means of long- 
handled rakes operated by men in boats, or they 
are secured by divers. They are then spread out on the shore in the sun, 
where bacteria cause the tissues to decay; then after treatment consisting 
of beating, bleaching, and trimming, the bath sponge is ready for the 
market. 

Coelenterates 

The hydra and its salt- water allies, the jellyfish, hydroids, and corals, 
belong to a group of animals known as the Ccelentera'ta. The word " coe- 
lenterate" (coelom = body cavity, enter on = food tube) explains the struc- 

^ The matter in small type in this and other parts of the book is intended 
largely as reference and outside reading or project reference reading. There 
are always some members of a class who have interests more keenly biological 
than others. It is thought that these pages may be particularly usefizl for such 
students. These pages will also be useful when they describe material that 
can be found locally and used in the laboratory. 




Venus's flower basket; a 
sponge with a glassy skel- 
eton. 



190 SIMPLE METAZOA — DIVISION OF LABOR 



ture of the group. They are animals in which the real body cavity is lack- 
ing, the animal in its simplest form being little more than a bag. 

Medusa. — Among the most interesting of all the coelenterates inhabit- 
ing salt water are the jellyfishes or medusae. These animals vary greatly 

in size from a tiny umbrella- 
shaped form little larger than 
the head of a pin to huge jelly- 
fishes several feet in diameter. 



Tentdcle 
food tube 




Mouth 



V-Tentdde 




Medusa or jellyfish. Photograph 
from American Museum of Natural 
History. 



A hydroid colony of six polyps: 
/, feeding polyp; r, reproductive 
polyp; m, a medusa; y, young 
polyp. 



Development. — Many species of medusse pass through another stage of 
life. As medusae they reproduce by eggs and sperms, that is, sexually. 
The egg of the medusa segments, forming ultimately a ball of cells (the 
hlastula) which swims around by means of cilia. Ultimately the little ani- 
mal settles down on one end and becomes fixed to a rock, seaweed, ot 
pile. The free end becomes indented in the same manner as a hollow 
rubber ball may be pushed in on one side. This indented side becomes a 
mouth, tentacles develop around the orifice, and we have an animal that 
looks very much like the hydra. This animal, now known as a hydroid 
polyp, buds rapidly and soon forms a colony of little polyps, each of which 
is connected with its neighbor by a hollow food tube. The hydroid polyp 
differs from its fresh-water cousin, the hydra, by usually possessing a 
tough covering which is not alive. 



CCELENTERATES 



191 




Alternation of Generations in Coelenterates. — The lives of a hydroid 
poiyp and a medusa are seen thus to be intimately connected. A 
hydroid colony produces new polyps by budding. This is an asexual 
method of reproduction. There come from this hydroid colony, how- 
ever, Httle buds which give rise to free-swimming medusae. These 
medusae produce eggs and sperms. Their reproduction is sexual, as was 
the reproduction by means of eggs and sperms from the prothallus of 
the fern. So we have in animals, as well as in plants, an alternation of 
generations. 

Sea Anemone. — Those who have visited our New England coast are 
famihar with another coelenterate called the sea anemone (a-nSm'6-ne). 
This animal gets its name because, 
when expanded, it looks Hke a 
beautiful flower of a golden yellow 
or red color. The body of the 
sea anemone is like the hydra, a 
colunm attached at one end. The 
free end is proidded with a mouth 
surrounded with a great many 
tentacles. These, when ex- 
panded, look like the petals of a 
flower. The sea anemone is a 
very voracious animal, for by 
means of the batteries of stinging 
cells in its tentacles it is able to 
catch and devour fishes and other 
animals almost as large as itself. 
When disturbed, or irritated, the 
animal contracts into a sHmy ball which is difficult to dislodge from its 
attachment. 

Although the sea anemone is like a large hydra in appearance, its in- 
terior is different. The hollow digestive cavity contains a number of par- 
titions more or less complete, which run from the outer wall toward the 
middle of the cavity. These partitions, known as mes'enteries, are found 
in pairs. Part of the cavity, as in the hydra, is given up to digesting the 
food. Food is killed by means of stinging cells found in the long thread- 
Uke tentacles. 

Coral. — If a piece of madrepor'ic coral is examined with a hand lens, a 
number of httle depressions will be seen in the limy surface, each of which 
has tiny partitions within it. These cupHke depressions were once occupied 
by the coral animals of polyps, each in its own cup. The mesenteries of the 
coral polyp are paired and hollow on the under surface. The partitions 
seen in the coral cups lie between the pairs of mesenteries, and are formed 
bj'^ them when the animal is alive. Sea water has a considerable amount 
of hme in its composition. This lime (calcium carbonate) is taken from 
the water by certain of the cells of the coral polyp and deposited around 



Sea anemone. About one half natural 
size. The right-hand specimen is ex- 
panded. Note the mouth surrounded by 
the tentacles. The left-hand specimen is 
contracted. From model at the American 
Museum of Natural History. 



192 SIMPLE METAZOA — DIVISION OF LABOR 

the base of the animal and between the mesenteries, thus giving the 
appearance just seen in the cups of the coral branch. 

Asexual Reproduction. — These polyps reproduce by budding, and 
when alive cover the whole coral branch with a continuous Hving mass of 
polyps, each connected with its neighbor. In this way great masses of 
coral are formed. Coral, in a Hving state, is aUve only on the surface, 
the polyps building outward on the skeleton formed by their predecessors. 

Economic Importance of Corals. — Only one (astrangia) of a great 
many different species of coral hves as far north as New York. In tropical 
waters they are very abundant. Coral building has had and still has an 
immense influence on the formation of islands, and even parts of conti- 
nents in tropical seas. Not only are many of the West Indian islands 







•M». 


1 


f. 


w^^u 


^ps 


1 


^^ 




1 


^^ 


%^^?^^ W^ 


^^m^k 


^^^^m 




^:^^^ 


mmm 




WW 




A branching madreporic coral. 



A single coral cup, 
showing the walls of lime 
built by the mesenteries. 
From a photograph 
loaned by the American 
Museum of Natural His- 
tory. 



composed largely of coral, but also Florida and many islands of the 
southern Pacific are almost entirely of coral formation. 

Coral Reefs. — The coral polyps can live only in clear sea water of 
moderate depth. Fresh water, bearing mud or other impurities, kills 
them immediately. Hence coral reefs are never found near the mouths 
of large fresh-water rivers. Polyps are frequently found building reefs 
close to the shore. In such cases these reefs are called fringing reefs. 
The so-called barrier reefs are found at greater distance (sometimes forty 
to fifty miles) from the sliore. An example is the Great Barrier Reef of 
Australia. The typical coral island is called an atoU. It has a circular 
form inclosing a part of the sea which may or may not be in communica- 
tion with the ocean outside the atoll. The atoll was perhaps at one time 
a reef outside a small island. This island disappeared, probably by the 
sinking of the land. The polyps, whi(;h could live in water up to about 
one hundred and fifty feet, continued to build the reef until it rose to 
the surface of the ocean. As the polyps could not exist for long above low- 
waterline, the animals died and their skeletons became disintegrated by 



SIMPLE METOZOA 193 

the action of waves and air. Later birds brought a few seeds there, per- 
haps a coconut was washed ashore; thus plant life became established in 
the atoll, and a new outpost to support human life was established. 

A Simple Classification of Ccelenterates 

Class I. Hydrozo'a. A simple body cavity containing no mesenteries, usually 
alternation of generations. Examples: Hydra, hydroids. 

Class II. Scyphozoa (sl-fo-zo'a). Example: large jellyfishes. 

Class III. Actinozo'a, Mesenteries present in body cavity. Examples: 
sea anemones and corals. 

Class IV. Ctenophora (te-nQf'o-ra). 

Summary. — All animals develop from egg cells, which, after 
fertilization, go through a series of divisions. A hollow ball of 
cells (the blastula) is formed, and then a cup-shaped mass (the 
gastrula). Some animals such as the hydra stop their develop- 
ment at this stage; others reach a more complex adult stage. 

The animals in the group coelenterata have certain character- 
istics in common. One is the possession of stinging cells. Can 
you find any other characteristics which they all have? 

Physiological division of labor has been shown to be the per- 
formance of different kinds of work by different collections of 
cells in an organism. This is shown in a simple way in the hydra. 

Problem Questions. — 1. Compare reproduction in a simple 
plant and in a simple animal. 

2. Describe the early stages of development in an animal. 

3. Describe the structure of a simple sponge. 

4. Compare the structure of a hydra and of a jellyfish. 

5. Explain alternation of generations. Where have you found 
it before? 

6. Discuss the economic importance of three animals men- 
tioned in this chapter. 

Problem and Project References 

Calkins, Biology. Henry Holt and Company. 

Hegner, Introduction to Zoology. The Macmillan Company. 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Miner, A Guide to the Sponge Alcove. Guide Leaflet, No. 23. American Museum 

of Natural History, New York. 
Parker, Lessons in Elementary Biology. The Macmillan Company. 
Sedgwick and WUson, General Biology. Henry Holt and Company. 
Shull, Principles of Animal Biology. McGraw-Hill Book Company, 
Sharpe, A Laboratory Manual. American Book Company. 



XVII. THE WORMS, A STUDY OF RELATIONS 
TO ENVIRONMENT 

Problem. To discover the relation of the earthworm to its sur- 
roundings. (Laboratory Manual, Prob. XXVII; Laboratory 
Problems, Prob. 118.) 

Effect of Surroundings on Plants. — Animals as well as plants 
are influenced ver}^ greatly by their surroundings or environ- 
ment. We have seen how green plants behave toward the 
various factors of their environment; how heat and moisture 
start germination in a seed; how the roots grow toward water; 
how gravity influences the root and the stem, pulling the root 
downward and stimulating the stem to grow upward; how the 
stem grows toward the source of Hght; and how the leaves put 
their flat siu-faces so as to ^et as much hght as possible; . and 
how oxygen is necessary for life to go on. 

It is quite possible to show that the factors of environment 
act upon animals as well as plants, although it is much harder 
to explain why an animal does a certain thing at a certain time. 

How One-celled Animals respond to Stimuli. — We have seen 
that the single-celled animals respond to certain stimuh in their 
surroundings. The presence of food attracts them; when they 
run into an object, they respond immediately by backing away, 
thus showing that they have a sense of touch. If part of a 
glass slide containing paramecia is heated slightly, the ani- 
mals will respond to the increase in heat bj^ moving toward 
the cooler end. Other experiments also might be quoted to 
show that the living matter of a simple animal is sensitive to 
its surroundings. 

The Earthworm in its Relation to its Surroundings. — The 
earthworm, familiar to most bo3^s as bait, shows us in many 
ways liow a many-celled animal responds to stimuli. Careful 
observation of the body of a living earthworm reveals that 
its long tapering body is made up of a large number of ringr. 

194 



THE EARTHWORM 195 

OP segments. The number of these segments will be found to 
vary in worms of different lengths, the loJiger earthworms having 
more segments. 

If the two ends of the earthworm be touched hghtly with a small 
stick or straw, one end wiU be found to respond much more 
readily to touch than the other end. The more sensitive end 
is the front or anterior end; the other end is the posterior end. 
Jar the dish in which the earthworm is crawling; it will inune- 
diately respond by contracting its body. 

Living earthworms tend to coUect along the sides of a dish 




An eaT-tliworm crawling over a smooth surface. 

or in the corners. This seems to be due to an instinct which 
leads theni to inhabit holes in the ground. 

An earthworm placed half in and half out of the darkened area 
in a box soon responds by crawling into the darkened part and 
remaining there. It has no eyes visible. A careful study of the 
worm with the microscope, however, has revealed the fact that 
scattered through the skin, particularly^ of the anterior seg- 
ments, are many little structures which enable the animal to 
distinguish not only between light and darkness, and between 
light of low and high intensity, but also the direction from which 
it comes. An earthworm has no ears or special organs of feel- 
ing. We know, however, that it responds to vibrations of low 
intensity, and the sense of touch is well developed in all parts 
of its body. 

It also responds to the presence of food, as can be proved if 
bits of lettuce or cabbage leaf are left overnight in a dish of 
e^rth where earthworms axe kept. 



196 



WORMS 




ty 



Locomotion of an Earthworm. — If we measure an earthworm 
when it is extended and compare with the same worm con- 
tracted, we note a difference in length. This is accounted for 
when we understand the method of locomotion. Under the 
skin are two sets of muscles, an outer set which passes in a 
circular direction around the body, and an inner set which runs 
the length of the body. The body is lengthened by the con- 
traction of the circular muscles. How might the body be 
shortened? 

The under surface of the earthworm is provided with four double 

rows of tiny bristles called 
8e!t(B, on all the segments 
except the first three and the 
last. Each seta has att,« ?hed 
to it small muscles, which 
tUxQ it so it may point 
in the direction opposite to 
that in which the worm is 
moving. If you watch a 
specimen carefully, you will 
see that locomotion is ac- 
complished by the thrusting 
forward of the anterior end, followed by a wave of muscular 
contraction passing down the body, thus shortening the body by 
drawing up the posterior end. The setae at the anterior end serve 
as anchors which prevent the body from slipping backward as the 
posterior end is drawn up. 

How the Earthworm digs Holes. — A feeding earthworm will 
show the prosto'mium, an extension of the upper lip which is used 
as an organ of sensation. The earthworm is not provided with 
hard jaws or teeth. Yet it literally eats its way through the 
hardest soil. Behind the mouth opening is a part of the food 
tube called the phar^ynx. This is very muscular so that it can 
be extended and withdrawn by the earthworm. When applied to 
the surface of the soil, which is first moistened by the earthworm, 
it acts as a suction pump and draws particles of the soil into the 
food tube. In order to take organic matter out of the ground as 
food, the earthworms pass the earth through the body. The earth 



Diagram to show how Tnovement of a 
seta is accomplished; M, muscles; S, 
seta; W, body wall. (After Sedgwick 
and Wilson.) 



THE EARTHWORM 



197 



is mixed with fluids poured out from glands in the food tube, 
which digest the food, and the soil is passed out of the body and 




-^ Upper Up 
-Br din 
-Pharynx 

Aortic arch 
^ Mlet 



deposited on the surface of 
the ground, in the form of 
little piles of moist earth. 
These are familiar sights on 
all lawns; they are called 
worm casts. Charles Darwin 
calculated that fifty-three 
thousand worms may be found 
in an acre of ground, that ten 
tons of soil might pass through 
their bodies in a single year 
and thus be brought to the 
surface, and that they plow 
more soil than all the farmers 
put together. 

Comparison between Hydra and 

Earthworm. — The digestive tract of 

the earthworm is an almost straight 

tube inside of another tube. The 

latter is divided by partitions which 

mark the boundary of each segment. 

The outer cavity is known as the body cavity. In the hydra no body cavity 

exists, there being only a digestive cavity. In the animals higher than the 

Qcelenterates the digestive tract and body cavity are distinct. Food is 

digested within the food tube, 
is passed through the walls of 
this tube into the body cavity, 
and is carried by the blood to 
various parts of the body. 
The earthworm has no gills or 
lungs, the thin skin acting as 
an organ of respiration. But 
the earthworm is unable to take 
in oxygen unless the mem- 
branehke skin is kept moist. 



-Crop 
-Gizzard 

"Stomach - Intestine 
-Bloodvessel 



Fore part of an earthworm opened on 
the dorsal side to show the body cavity 
and food tube within it. 




Diagrammatic cross section of the body of a 
coelenterate, and that of a worm. 



Development. — The earthworm has both male and female 
sex cells present in its body and hence is said to be hermaphro- 
dific (from Hermes and Aphrgdito)' In order to have the eggs 



198 WORMS 

fertilized when they are laid a mutual exchange of sperm cells 
takes place between two worms, the sperms being placed in 
four little sacs on the ventral side of each worm. Later the 
swollen area called the girdle (about one third the distance from 
the anterior end) forms a httle sac in which the eggs of the worm 
are laid. As this sac passes toward the anterior end of the 
earthworm it receives from the body openings the sperms which 
were received from the other earthworm and a nutritive fluid 
in which the eggs Hve. The fertihzed eggs are then left to 
hatch. The sacs or capsules may be found in manure heaps, 
or under stones, in May or June; they are small yellowish or 
brown bags ab'^ut the diameter of a worm. 

Regeneration. — If a one-celled animal be cut into two 
pieces, each piece, if it contains part of the nucleus, can grow 
into a whole cell. The hydra, some hydroids, jellyfish, and flat- 
worms, if injured, may grow again parts that are lost. This 
power is known as regeneration. Earthworms possess to a large 
degree the power of replacing parts lost through accident or 
other means. The anterior end may form a new posterior end, 
while the posterior end must be cut anterior to the girdle to 
form a new anterior end. This difference seems to be due in 
part to the greater complexity of the organs in the anterior end. 

Other Segmented Worms. — The sandworm, living on tidal 
flats along our eastern coast, is a common sight to those who 
live in that region. The leech or bloodsucker is a form known 
to every small boy who has bathed in a fresh-water pond. 
Discomfort, but no danger, attends the bite of this worm. 

Problem. To determine some harmful animal associations, 
{Laboratory Manual, Prob. XXVIII.) 

Some "Worms which harm Man. — Some worms are unseg- 
mented; such are the flatworms and roundworms. A common 
leaflike form of flatworm may be found clinging to stones in 
our fresh-water ponds or brooks. Most flatworms are, however, 
parasites on other animals; that is, they obtain food and 
shelter from some other living creature, but give it no benefits 
in return. Parasitism is one-sided, the host giving everything, 
the parasite receiving everything. Consequently, the parasite 




WORMS WHICH HARM MAN 199 

frequently becomes fastened to its host during adult life and 
often is reduced to a mere bag through which the fluid food 
prepared by its host is absorbed. Such animals as have lost 
power to move about freely, to digest food, or to perform some 
other function as a result of their 
comfortable surroundings, are said to 
have degenerated. 

Sometimes a complicated life history 
has arisen from parasitic habits. 
Such is seen in the hfe history of the 
liver fluke, a flatworm which kills a flatworm iYungm au- 

sheep, and in the tapeworm. rantiaca), much magnified. 

, From model in the American 

Cestodes or Tapeworms. — ihese Museum of Natural History. 

parasites infest man and many other 

vertebrate animals. The tapeworm (Tcrnia solium) passes 
through two stages in its life history, the first within a pig, 
the second within the intestine of man. The eggs of this worm 
are 'taken in with the pig's food. The young worm develops 
within the intestine of the pig, but soon makes its way into 
the muscles. When man eats pork containing tapeworms, if the 
pork has not been sufficiently cooked, he may become a host 
for the tapeworm. Another common tapeworm parasitic on 
man lives part of its life as an embryo within the muscles 
of cattle. The adult worm consists of a round headlike part 
provided with hooks, by means of which it fastens itself to 
the walls of the intestine. This head now buds off a series 
of segmentlike structures, which are practically bags full of 
eggs. These structures, called progloftids, break off from time 
to time, thus allowing the eggs to escape. A proglottid 
has no separate digestive system, but the whole body surface 
is bathed in digested food, which it absorbs and thus the para- 
site is enabled to grow rapidly. 

Roundworms. — Still other wormlike creatures called round- 
worms are of importance to man. Some, as the vinegar eel 
found in vinegar, or the pinworms parasitic in the lower intes- 
tine, particularly of children, do little or no harm. The pork 
worm or trichina (tri-ki'na), however, is a parasite which may 
cause serious injury. It passes through the first part of its 



200 



WORMS 



existence as a parasite in a pig or other vertebrate (as a cat, 
rat, or rabbit), where it encysts itself in the muscles of its hosts. 
If the meat is oaten in an uncooked condition, the cyst is dis- 
solved olT by the action of the 
digestive fluids, and the living 
trichina becomes free in the 
intestine. Here it bores its 
way through the intestinal 
walls and enters the muscles, 
causing inflammation. This 
results in a painful and often 
fatal disease known as trich- 
ino'sis. 

The Hookworm. — The ac- 
count of the discovery by 
Dr. C. W. Stiles of the 
Bureau of Animal Industry, 
that the shiftlessness of the 
"poor whites" of the South 
is due partly to a parasite 
called the hookworm, another 
roundworm, reads like a 
fairy tale. 
Effect of hookworm infection. The The people, largely farmers, 

young man at the left 17 yearsold, weighs bcCOmC infected with a 
156 pounds. His older brother beside 

him, 18 years of age, badly infected with larval Stage of the hookworm, 

hookworm, weighs only 74 pounds. which dcVClopS in m O i S t 

earth. It enters the body usually through a break in the 
skin of the feet, for children and adults alike, in certain local- 
ities where the disease is common, go barefoot to a consider- 
able extent. 

A complicated journey from the skin to the intestine now 
follows. The larvse pass through the veins to the heart, and from 
there to the lungs. They then bore into the air passages and 
eventually reach the intestine by way of the windpipe. One 
result of the injury to the lungs is that many thus infected are 
subject to tuberculosis. The adult hookworms, once in the food 
tube, fasten themselves to the walls, which they puncture, and 




THE HOOKWORM 201 

feed upon the blood of their host. The loss of blood from this 
cause is not sufficient to account for the bloodlessness of the 
[)erson infected, but a poison poured into the wound by the hook- 
worm prevents the blood from coagulating rapidly; hence a 
considerable amount of blood escapes from the wound after the 
hookworm has finished its meal and gone to another part of 
the intestine. 

The cure of the disease is very easy: th3Tiiol, which weakens 
the hold of the hookworm, followed by Epsom salts. For 
years the entire South undoubtedly has been retarded in its 
development by this parasite. Hundreds of millions of dol- 
lars have been wasted, and, what is more vital, thousands of 
lives have been needlessly sacrificed. 

" The hookworm is not a bit spectacular: it doesn't get itself discussed 
in legislative halls or furiously debated in political campaigns. Modest 
and unassuming, it does not aspire to such dignity. It is satisfied simply 
with (1) lowering the working efficiency and the pleasure of hving in some- 
thing like two hundred thousand persons in Georgia and all other Southern 
states in proportion; with (2) amassing a death rate higher than tuber- 
culosis, pneumonia, or typhoid fever; with (3) stubbornly and quite effec- 
tually retarding the agricultural and industrial development of the section^ 
with (4) nullifying the benefit of thousands of dollars spent upon educa- 
tion; with (5) costing the South, in the course of a few decades, several 
hundred millions of dollars. More serious and closer at hand than the 
tariff; more costly, threatening, and tangible than the Negro problem; 
making the menace of the boll weevil laughable in comparison — it is pre- 
eminently the problem of the South." — Atlanta Constitution. 

The work of the Rockefeller Foundation in the tropics has 
proved that the hookworm is found in most hot and moist cli- 
mates and that consequently natives of such countries are often 
attacked by it. It is thought that 75 per cent of the natives 
of Southern China, 60 to 80 per cent of 300,000,000 natives 
of India and over 90 per cent of the laboring classes of Dutch 
Guiana and Colombia are infected with it, while over 2,000,000 
pectpie in this country are its victims. If we were to estimate the 
economic loss due to hookworm the world over, it would run into 
hundreds of millions of dollars annually. 

Other Parasitic Worms. — Somie roundworm parasites live in 
Hunt. New Ee. — 14 



202 WORMS 

the skin, and others live in the intestines of the horse. Still 
others are parasitic in fish and in insects, one of the common- 
est being the hair snake, often seen in country brooks. 

A Simple Classification of Worms 
A. Segmented Worms (Annula'ta) 

Class I. C/itefoporfa (k^-t6p'o-da; bristle-footed). Segmented worms having 

setae. 
Subclass I. Polychceta (p6l-i-ke'ta; many bristles). Having parapodia, 

and usually head and gills. Example: sandworm. 
Subclass II. Oligochoe'ta (6l-i-go-ke'ta; few bristles). No parapodia, 

head, or gills. Example: earthworm. 
Class II. Discophora (dls-k6f'6-ra; bearing suckers). No bristles, two 

sucking disks present. Example: leech. 

B. Flatworms 

Body flattened in dorso-ventral direction 
Class I. Turbella'ria. Small, aquatic, mostly not parasitic. Example: 

planarian worm. 
Class II. Tremato'da. Usually parasitic worms which have complicated 

life history. Example: liver fluke of sheep. 
Class III. Cesto'da. Internal parasites having two hosts. Example; 

tapewonn. 

C. Roundworms 

Threadlike worms, mostly parasitic. Examples : vinegar eel, trichina, 
and hookworm. 

Summary. — The earthworm is a simple type of a segmented 
worm. One of its most important differences from the hydra 
lies in its possession of a body cavity as well as a digestive 
cavity. 

Parasitic worms such as the tapeworm, trichina, and hook- 
worm play an important economic part in the life of today. 
Thanks to the work of the Rockefeller Foundation and other 
agencies, hookworm disease is fast being reduced in all civilized 
parts of the earth. 

Problem Questions. — 1. How is the earthworm of economic 
importance ? 



WORMS 203 

2. Describe the internal structure of the earthworm and tell 
the use of each part named. 

3. Discuss the life history of some parasitic worm and show 
how its harmfulness may be combated. 

Peoblem and Project References 

Darwin, Formation of Vegetable Mould. D. Appleton and Company. 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Hunter and Whitman, Civic Science. American Book Company. 

Reports of the Rockefeller Foundation. 

Ritchie, A Primer of Sanitation. World Book Company. 

Sedgwick and Wilson, General Biology. Henry Holt and Company. 

Sharpe, A Laboratory Manual. American Book Company. 



XVIII. THE CRAYFISH. A STUDY OF ADAPTATIONS 

Problem. A study of the meaning of the term of adaptation as 
shown in the crayfish. (Laboratory Manual, Prob. XXIX; 
Laboratory Problems, Prob. 118.) 

(a) Protection. 

(b) Locomotion. 

(c) Feeding. 

(d) Breathing. 

Adaptations. — Plants and animals are in a continual struggle 
to hold the places they have obtained upon the earth. Con- 
tinually we see garden plants driven out or killed by the com- 
peting weeds, simply because the weeds are better fitted or 
adapted to live under the conditions which exist in the garden, 
especially if it is uncultivated. An adaptation in a plant or 
animal is some change in structure, habit, or ability which is of 
advantage to the organism in its battle for life. We have 
seen many examples of adaptations in plants, — adaptations in 
flowers for securing cross-pollination, in fruits for seed-scatter- 
ing, in young plants for protection, in roots for securing water; 
the list is endless. 

In animals, likewise, the successful competitors are the ones 
with adaptations to fit them for living in the particular environ- 
ment or surroundings in which nature has put them. Examples 
are often seen where animals, like sheep or goats, which have 
a woolly covering, when introduced by man into a warmer 
country, die because the outer coat is too warm. An adaptation 
for withstanding cold becomes harmful to the animal in a 
warmer country. 

One adaptation which we have already noticed in animals is 
always protective. This is the resemblance of the animal to the 
surroundings in which it lives. Other adaptations aid the ani- 
mal in obtaining aucj digesting food, in protecting itself or its 

m 



A STUDY OF ADAPTATIONS 



205 



young from attacks by enemies, and in battling successfully with 
the dangers around it. 

The Crayfish. Adaptations for Protection. — Animals which 
illustrate adaptations for hfe in the water are the fresh-water 
crayfish and the salt-water lobster, both members of a large 
group of animals known as crusta'ceans. The body of one of 
these animals is seen to be encased more or less completely in 
a hard covering, which is jointed in the posterior region. This 
exoskeleton (outside skeleton) is composed largely of Hme, as 
may be proved by testing with acid. The exoskeleton fits over 
the anterior part of the animal, forming an un jointed car' apace, 




Crayfish: A., antennae; E., stalked eye; C.P., cephalotho^ax; Ab., abdomen; 
C.F., caudal fin; M., mouth; Ch., chelipeds. From photograph. 

or armor. This armor is clearly protective and is therefore an 
adaptation. If the crayfish is watched in a balanced aquarium, 
the colors are seen to blend remarkably with the stones and 
water weeds of the bottom. The animal is protectively col- 
ored. The under side of the animal is less well protected than 
the upper, and the joints of the abdo'men, or posterior region, 
extend completely around the body. The animal is segmented, 
the abdomen showing the segments plainly. 

Locomotion. — Those of us who have caught crayfish in fresh- 
water streams or lakes know that it takes skill and quickness. 
They dart backwards through the water with great rapidity, 
or they move forward by crawling on the bottom. Examina- 
tion of a crayfish shows us five pairs of walking legs attached 
to the under side of the cephalotho'rax (head + thorax), the 



20G 



THE CRAYFISH 



anterior part of the body. These legs are jointed, and the first 
tliree pairs bear pinchers. Tlie hirge pinchcr claws or chelipeds 
(ke'li-pedz) arc used for food-catching as well as for locomo- 
tion. Try to find out exactly what then- use is in a Hving 
specimen. 

Under the abdom6n, one pair on each segment except the last, 
are found jointed appendages, made up of three parts, a base 

and two branches. These 
are called swimmer ets, 
though they are not used 
for swimming. Now look 
at the broad pair of 
swimmerets which, to- 
gether with the last 
segment of the abdomen, 
form a finlike apparatus, 
XhQ caudal fin. Crayfish 
swim very rapidly by 
means of a sudden jerk- 
ing of the caudal fin in 
a backward direction. 
The abdomen is pro- 
vided with powerful 
muscles which are at- 
tached to the exo- 
skeleton. It is by these 
muscles that the rapid 
swimming is accom- 
plished. 
How the Crayfish gets in Touch with its Surroundings. — 
Several other appendages besides those used for locomotion are 
found. Two pairs of " feelers," the longer pair called the 
anten'nce, the shorter the anten'nules (httle antennae), protrude 
from the front of the body. The longer feelers appear to be 
used as organs of touch and smell. The smaller antennules 
hold at their bases little sacs called balancing organs. 

Just above the antennules, projecting on stalks, are the eyes. 
These eyes are made up of many small structures called om- 




Female lobster, showing eggs attached to 
the swimmerets. From photograph loaned^ by 
the American Museum of Natural History. 



A STUDY OF ADAPTATIONS 



207 



matid'ia, each one of which is a very simple eye. A collection of 
ommatidia is known as a compound eye. Such an eye probably 
does not have very distinct vision. A crayfish, however, easily 
distinguishes moving objects and prefers darkness to Hght, as 
may be proved by experiment. 

Feeding. — Living food is obtained with the aid of the cheli- 
peds and shoved toward the mouth. It is pushed on by three 
pairs of small appendages called foot jaws or maxil'lipeds, and 




Appenda^ges of the crayfish: 1, antennule; 2, antenna; 3, mandible; 
4, first maxilla; 5, second maxilla; 6, first maxilliped; 7, second maxilliped; 
8, third maxiUiped; 9, cheliped; 10, 11, 12, i 5, walking legs; 14^, modified 
swimmeret in male; 15, modified swimmeret in male; 16, 17, 18, swimmerets 
which carry the eggs in female; 19, uropod, the side part of the caudal fin. 

to a slight degree by two still smaller paired maxiVlce just 
under the maxillipeds. Ultimately the food reaches the hard 
jaws and, after being ground between them, is passed down to 
the stomach. 



Experiment to demonstrate Breathing. — The mouth parts of a crayfish 
resting in the aquarium are observed to be constantly in motion, despite 
the fact that no food is present. If a crayfish is taken out of the water 
and held with the ventral surface uppermost, a little carmine (mixed in 
water) may be dropped on the lower surface and allowed to run down under 
the carapace. If the animal is now held in water in the same position, 
the carmine will reappear from both sides of the mouth, seemingly pro- 



208 



THE CRAYFISH 



pelled forward by something which causes it to emerge in little puffs. K 
we remove the maxillipeds and maxillae from a dead specimen, we find a 
groove leading back from each side of the mouth to a ca\'ity of consider- 
able size on each side of the body under the carapace. This is the gill 
•chamber. It contains the gills, the organs which absorb the oxygen dissolved 
in the water. The second maxillae are prolonged into the groove to serve 
as bailers or scoops. By rapid action of these organs a current of water is 
maintained which passes over the gills. 

The Gills. — The gills are outside of the body, although pro- 
jected by the carapace. If the carapace is partly removed on 




Crayfish with the left half of the body structures removed: a, intestine; 
6, ventral artery; c, brain; e, heart; et, gastric teeth; i, oviduct; I, diges- 
tive gland; m, muscles; n, green gland (kidney); o, ovary; p, pjdoric 
stomach; r, nerve cords; s, cardiac stomach; st, mouth; u, telson, or 
last segment of the abdomen, forming the middle part of the caudal fin; 
w, openings of veins into the pericardial sinus. Natural size. (Davison, 
Zoology.) 



one side, they will be found looking somewhat like white 
feathers. The blood of the crayfish passes by a series of veins 
into the long axis of the gill,' where the blood vessels divide 
into very minute tubes, the waUs of which are extremely deli- 
cate. Oxygen, dissolved in the water, passes into the blood by 
osmosis, during which process the blood loses some carbon 
dioxide. The gills are kept from drying by being placed in a 
nearly closed chamber, which has a row of tiny hairs bordering 
the lower edge of the carapace. Thus crayfish may live for 
long pei-iods away from water. 

Circulation. — The circulation of blood in the crayfish takes place In 
a system of thin-walled, flabby vessels which are open in places, allowing 
the blood to come in direct contact with the tissues to which it flows. 
The heai't lies on the dorsal side of the bodv, inclosed in a delicate bag, 



A STUDY OF ADAPTATIONS 209 

toto which all the blood in the body eventually finds its way during its 
circulation. 

Digestion. — Food which has not been ground up previously into pieces 
smaU enough for the purpose of digestion is still further masticated by 
means of three strong projections or teeth, one placed on the mid-line and 
two on the side walls of the stomach. The exoskeleton of the crayfish 
extends into the stomach, thus forming the gastric mill just described. 

The stomach is divided into anterior and posterior parts separated 
from each other by a constriction. The posterior part is lined with tiny 
projections from the walls which make it act as a strainer for the food 
passing through. Thus the larger particles of food are kept in the an- 
terior end of the stomach. Opening into the posterior end of the stomach 
are two large digestive glands whose juices further prepare the food for 
absorption through the walls of the intestine. Once in the blood, the fluid 
food is circulated through the body to the tissues which need it. 

Nervous System. — The internal nervous system of a crayfish con- 
sists of a series of collections of nerve cells called ganglia (gS-ng'gll-a) con- 
nected by means of a double line of nerves. Posterior to the gullet, this 
chain of ganglia is found on the ventral side of the body, near the body 
wall. At the anterior end it encircles the gullet and forms a brain in the 
head region, from several ganglia which have grown together. From each 
of these ganglia, nerves pass off to the sense organs and into the muscles 
of the body. These nerve fibers are of two sorts, those bearing messages 
from the outside of the body to the central nervous system (these messages 
result in sensations), and those which take outgoing messages from the 
central nervous system (motor impulses), which result in muscular move- 
ments. 

Development. — The sexes in the crayfish are distinct. The eggs are 
fertilized by the sperm cells as they pass to the outside of the body of the 
female. The eggs, which are provided with a considerable supply of food 
material called yolk, are glued fast to the swimmerets of the mother, and 
there develop in safety. The young, when they first hatch, remain 
clinging to the swimmerets for several weeks. 

Excretion of Wastes. — On the basal joint of the antennae are found two 
projections, in ihe center of which are tiny holes. These are the open- 
ings of the green glands, organs which eliminate the nitrogenous waste from 
the blood, the function of the human kidneys. 

a 

North American Lobster. — In structure the lobster is almost 
the counterpart of its smaller cousin, the crayfish. Its geographi- 
cal range is a strip of ocean bottom along our coast, estimated 
to vary from thirty to fifty miles in width. This strip extends 
from Labrador on the north to Delaware on the south. The 
lobster is highly sensitive to changes in temperature. It mi- 



210 



THE CRAYFISH, ETC. 



grates from deep to shallow water, or vice versa, according to 
changes in the temperature of the water, which in winter is 
relatively warmer in deep water and cooler in shallows. Sudden 
changes in the temperature of the water of a given locality may 
cause them to disappear from that place. The food supply 

which is more abundant near the shore 
also aids in determining the habitat 
of the lobster. Lobsters do not appear 
to migrate north and south along the 
coast. While little is known about 
their habits on the ocean bottom, it 
is thought that they construct burrows 
somewhat like the crayfish, in which 
they pass part of the time. As they 
are the color of the bottom and as 
they pass much of their time among 
the weed-covered rocks, they are able 
to catch much living food, even active 
fishes falling prey to their formida- 
ble pinchers. They move around 
freely at night, usually remaining 
quiet during the day, especially when 
in shallow water. They eat some 
dead food and thus are scavengers; 
the same is true of the crayfish. 

Development. — The female lobsters 
begin to lay eggs when about seven 
inches in length. I^obsters of this 
size lay nearly five thousand eggs; this number is increased to 
about ten thousand by lobsters of moderate size (ten inches in 
length); by exceptionally large specimens as many as one 
hundred thousand eggs are sometimes laid. The eggs are laid 
every alternate year, usually during the months of July and 
August. Eggs laid in these months, as shown by observations 
made along the coast of Massachusetts, hatch the following 
May or June. The eggs are provided with a large supply of 
yolk (food), the development of the young animal taking place 
at the expense of this food material. After the young escape 




North American lobster. 
This specimen, preserved at 
the U. S. Fish Commission at 
Woods Hole, was of unusual 
size and weighed over twenty 
pounds. Notice the chelipeds. 



THE LOBSTER 211 

from the eggs, they are almost transparent and little like the 
adult in form. During this period of their lives the mortality 
is very great, as they are the prey of many fish and other free- 
swimming animals. It is estimated that barely one in five 
thousand survives this period of peril. At this time they grow 
rapidly, and in consequence are obliged to shed their exoskeleton 



Metamorphosis of a lobster: 1, 2, 3, larval stages; 4, very young lobster in its 

adult form. 

(molt) frequently. During the first six weeks of life, when they 
swim freely at the surface of the water, they molt five or six 
times. ^ 

Molting. — During the first year of its life the lobster molts 
from fourteen to seventeen times. During this period it attains 
a length of from two to three inches. Molting is accomplished 
in the following manner: The carapace is raised up from the 
posterior end and the body is then withdrawn through the open- 
ing between it and the abdomen. The most wonderful part 
of the process is the withdrawal of the flesh of the large claws 
through the very small openings which connect the limbs with 
the body. The blood is first withdrawn from the appendage; 
this leaves the flesh in a flabby, shrunken condition so that 
the muscles can be drawn through without injury. The lobster 
also molts the lining of the digestive tract as far as the posterior 
portion of the stomach. Immediately after molting the lobster 
is in a helpless condition, and is more or less at the mercy of 
its enemies until the new shell, v/hich is secreted by the skin, 
has grown. 

1 Recent economic investigations upon the care of young lobsters show that 
animals protected during the first few months of free existence have a far bet- 
ter chance of becoming adults than those left to grow up without protection- 
Later in life they sink to the bottom, where, because of their protectively 
colored shell and the habit of hiding under rocks and in burrows, they are 
comparatively safe from the attack of enemies. 



212 



THE CRAYFISH, ETC. 




The edible blue crab. From photograph 
loaned by the American Museum of Natural 
History. 



Economic Importance. — The lobster is highly esteemed as 
food, and is rapidly disappearing fvom our coasts as the result 

of overfishing. Between 
twenty million and thirty 
million a year are taken 
on the North Atlantic 
coast. Laws have been 
enacted in New York 
and other states against 
overfishing. Egg-carry- 
ing lobsters must be re- 
turned to the w^ater; aU 
smaller than six to ten 
and one half inches in 
length (the law varies in different states) must be put back; 
other restrictions are placed upon the taking of the animals, in 
hope of saving the race from extinction. Some states now hatch 
and care for the young for a period of time; the United States 
Bureau of Fisheries is also doing 
much good work, in hope of 
restocking to some extent the 
now almost depleted waters. 

Shrimps. — Several other common 
crustaceans are near relatives of the 
crayfish. Among them are the 
shrimps and prawns, thin-shelled, ac- 
tive crustaceans common along our 
eastern coast. In spite of the fact 
tnat they form a large part of the 
food supply of many marine animals, Hermit crab, about twice natural 

especially fishes, they do not appear size. From photograph loaned by 
to be decreasing in numbers. Be- 
sides this value as a food for fishes, 
they are also used by man, the shrimp fisheries in this country aggregating 
over $1,000,000 yearly. 

The Blue Crab. — Another edible crustacean of considerable economic 
importance is the blue crab. Crabs are found inhabiting muddy bot- 
toms; in such localities they are caught in great numbers in nets or traps 
baited with decaying meat. They are, indeed, among our most valuable 
sea scavengers, although they are also hunters of living prey. The ante- 




the American Museum of Natural 
History. 



CRABS 



213 




The fiddler crab. From photograph 
loaned by the American Museum of 
Natural History. 



They 



rior part of the body of the crab is short and broad, being flattened dorso- 

ventrally. The abdomen is much reduced in size. Usually it is carried close to 

the under surface of the cephalo- 

thorax. In the female the eggs are 

carried under the ventral surface of 

the abdomen, fastened to the rudi- 
mentary swimmerets in the position 

which is usual for other crustaceans. 

The young crabs differ considerably 

from the adult in form and method 

of life. They undergo a complete 

metamor'phosis or change of form 

during development. Immediately 

after molting, crabs are greatly desired by man as an article of food 

are then known as " shedders," or soft-shelled crabs. 
Other Crabs. — Other crabs found along the New York coast are the 

prettily colored lady crabs, 
often seen running along our 
sandy beaches at low tide; 
the fiddler crabs, interesting 
because of their burrows and 
gregarious habits; and per- 
haps most interesting of all, 
the hermit crabs. The hermit 
crabs use the shells of snails 
as homes. The abdomen is 
soft, and unprotected by a 
limy exoskeleton, and has 
adapted itself to its condi- 
tions by curhng around in 
the spiral snail shell, so that 
it has become asymmetrical. 
These tiny crabs are great 
fighters and wage frequent 
duels with each other for 
possession of the more desira- 
ble shells. They exchange 
their borrowed shells for 




Giant spider crab from Japan. From pho- 
tograph loaned by the American Museum of 
Natural History. 



larger ones as growth forces them from their first homes. 

The habits of these animals, and those of the fiddler crabs, might be 
studied with profit by some careful boy or girl who spends a summer at 
the seashore and has the time and inclination to devote to the work. Of 
especial interest would be a study of the food and feeding habits of the 
fiddler crabs. 

A deep-water crab often seen along Long Island Sound is the spider 
crab, or " sea spider," as it is incorrectly called by fishermen. This ani- 



214 THE CRAYFISH 

mal, with its long spider-like legs, is neither an active runner nor swimmer; 
it is, howev^er, colored Hke the dark mud and stones over which it crawls; 
thus it is enabled to approach its prey without being noticed. The re- 
semblance to the bottom is further heightened by the rough body covering, 
which gives a hold to which seaweeds and sometimes such animals as barna- 
cles, hydroids, or sea anemones fasten themselves. 

A spider crab from the Sea of Japan is said to be the largest crustacean 
in the world, some specimens measuring eighteen feet from tip to tip of the 
first pair of legs. 

Symbiosis. — Certain of the spider crabs, as well as some of 
the larger deep-water hermit crabs, have come to live in a rela- 
tion of mutual helpfulness with hydroids, sponges, and sea 
anemones. These animals attach themselves to the shell of the 
crab and are carried around by it, thus receiving a constant 
change of location and a supply of food. What they do for 
the crab in return is not so evident, although one large Chinese 
hermit crab regularly plants a sea anemone on its big claw; when 
forced to retreat into its shell, the entrance is thus effectually 
blocked by the anemone. The living of animals in a mutually 
helpful relation has been referred to as symbiosis. Of this we 
have abeady had some examples in plants as well as among 
animals. (See page 169.) 

Habitat. — Most crustaceans are adapted to live in the water; 
a few forms, however, are found living on land. Such are the 
wood lice, the pill bugs, which have the habit of rolling up into 
a ball to escape attack of enemies, the beach fleas, and others. 
The coconut crab of the tropics climbs trees in search of food, 
returning to the water at intervals to moisten the gills. 

Characteristics of Crayfish and its Allies. — Our study shows 
us that animals belonging to the same group have several well- 
marked characteristics in common. The most important char- 
acteristic of the crusta'cea, the group to which the crayfish 
belongs, are the presence of a segmented limy exoskeleton, gills, 
jointed appendages, usually a pair to each segment of the body 
(except the last), stalked compound eyes, and the fact that they 
pass through a metamorphosis or change of form before they 
reach the adult state. 

Summary. — The crayfish has been used in this chapter to 
give us some idea of its numerous adaptations. These have 



A STUDY OF ADAPTATIONS 215 

to do with its method of locomotion, feeding, breathing, in fact 
all of its activities. Acts which tend to the preservation of the 
race may be adaptive as well as structures which have this 
purpose o 

Problem Questions. — 1. Explain what is meant by the term 
adaptation. 

2. Name and describe adaptations in the crayfish for protec- 
tion, feeding, breathing, locomotion, digestion. 

3. Is molting an adaptation? Explain. 

4. Discuss the life history of the lobster. 

5. Discuss the economic importance of the Crustacea, 

Problem and Project References 

Davison, Practical Zoology, pages 133-141. American Book Company. 

Herrick, The American Lobster. U. S. Fish Commission Report^ 1895. 

Huxley, The Crayfish. D. Appleton and Company. 

Jordan and Kellogg, Evolution and Animal Life. Chapter VIII. D. Appleton 
and Company. 

Mead, Reports on Lobster Industry. Rhode Island Inland Fisheries Commission. 

Parker and Haswell, Zoology, Chapters on Crustaceans. The Macmillan Com- 
pany. 

Snarpe, A Laboratory Manual. American Book Company. 



XIX. THE INSECTS 

Problem, A study of some animal likenesses and differences 
in order to understand an elementary classification oj insects. 
(Laboratory Manual, Prob. XXX; Laboratory Problems, Probs. 
8, 9, 10, 11,) 

(a) Grasshopper — a straight-winged insect, 

(b) Butterfly or moth — a scale-winged insect, 

(c) The typhoid fly — a two-winged insect. 

(d) A beetle — a sheath-winged insect. 

(e) A bug — a half -winged insect. 

(f) The dragon fly — a nerve-winged insect, 

(g) The bee — a membrane-ivinged insect. 
Qi) Summary of differences between orders. 
(i) Making a logical definition. 

Insects the Winners in Life's Race. — We are all familiar 
with common examples of insect life. Bees and butterflies we 
have already studied in connection with their work in the cross- 
pollination of flowers. Mosquitoes and flies all too often come 
to our notice as pests; the common household insects sometimes 
annoy us, while we often hear of and see in a small way the harm 
done by insects in the field and garden. Insects are a successful 
group. They outnumber all the other species of animals on the 
face of the earth. They hold their own in the air, in the water, 
and on the land. Fitted in many ways to lead a successful life, 
they have become winners in life's race. 

We have already, from our study of a bee, formed some idea 
of what an insect is. But it would be unfair to expect to know 
all insects from our slight knowledge of one form. Our object 
in the study of this chapter will be to get some first-hand 
knowledge of some common insects so that we may classify 
them and distinguish one from another. This great group, 
containing more than half of the known representatives of 
animal life on the earth, is made up of a number of groups 

216 



THE GRASSHOPPER 



217 



called orders. The insects contained in these orders have certain 
characteristics of structure and life history in common, yet each 
order differs somewhat from the other orders. The characteristics 
which all the groups possess in common give us a working 
definition of an insect. 

The Red-legged Grasshopper. — One of the most conunon in- 
sects in the United States is the red-legged grasshopper. Its 



Poster/or m'n^ Anterior wing head Compound eye 




Abdomen 
Spirede oms^ Segment 'f abdomen, 




^ -Antenna 
-/-Posiiion of ocellus 



\'(:v [Protfiom 

AMmthordx \\ Labium 
msthorax\ ^^emurofi^Jleg ymurofHeg 
Spiracle onhesothorax 
FemurofS-leg 



- -Labrum 
■Palpus 



Parts of the body of a male grasshopper. 

segmented body is divided into an anterior part, the head; a, 
middle portion, the tho'rax; and a posterior portion, the abdomen. 
The animal is nearly the color of the grass on which it lives. 
The tough exoskeleton covering the body is composed of chitin 
(kftin), a substance somewhat like that which forms the horns 
of a cow. 

The Thorax. — The thorax is formed of three segments, the 
most anterior of which is known as the protho'rax, the middle 
one as the mesothorax, and the 
posterior part as the metathorax. 
Each segment bears a pair of jointed 
legs, and the posterior two segments 
bear wings also. 

The Legs. — The legs, six in num- 
ber, are fitted for active hfe in 
the fields. A careful study of the insect shows the hind 
leg to be fitted for jumping, not only in structure but also 
in position. It is long, jointed, and attached to powerful mus- 
cles which enable the grasshopper to spring forward quickly to 

New Es. — 15 



remur 




TrochankrA 

Hind leg of a grasshopper. 



218 



THE INSECTS 




Cross section through the body of an in- 
sect: a, food tube; h, heart; n, nerve cord; 
/, spiracle, opening of trachea. 



a great distance when the size of its small body is considered. 

An examination of the foot or tarsus shows a number of tiny 

hooks and pads, by means of which the insect can cling to the 

swaying grass stalks. Study the other legs and see if you can 

find similar adaptive struc- 
tures. 

The Wings. — The mem- 
brane-like wings, when 
spread out, show differences 
in structure. The outer 
pair, stronger and narrower 
than the inner pair, serve 
to protect the latter. The 
inner wings, when not in 
use, fold up like a fan. 
The Abdomen. — The 

segmented abdomen does not bear appendages, but at the 

posterior end of the abdomen of the female are found paired 

movable pieces which together form the egg layer or ovipos'itor. 

The male grasshopper has a 

rounded abdomen. Mdncf/bfc 

Breathing Organs. — Ob- \ 

servation of the abdomen of 

a living grasshopper shows 

frequent movements of the 

abdomen. On each side of 

the abdomen in eight of the 

segments (in the red-legged 

grasshopper) are found tiny 

openings called spir'acles. 

These spiracles open into 

little tubes called tracheoe 

(tra'ke-e). The tracheae 

divide and subdivide like the 

branches of a tree, so that all parts of the body cavity are reached 

by their fine endings. Air is drawn in by the expansion of the 

abdomen and forced out when it contracts. The blood of an 

insect does not circulate through a system of closed blood tubes 




Max/7/ary 
Pa/pus 



Lab/alPd/pu5. 




Lab/i/m 



Mouth parts of a grasshopper. 



THE GRASSHOPPER 219 

as in man, but instead it more or less completely fills that part 
of the body cavity which is not occupied by other organs. By 
means of the tracheae, air is brought in contact with the blood, 
which takes in oxygen and gives off carbon dioxide. 

Muscular Activity. — Insects have the most powerful muscles 
of any animals of their size. Relatively, an enormous amount 
of energy is released during the jumping or flying of a grass- 
hopper. The tracheae pass directly into the muscles and other 
tissues so that a supply of oxygen is at hand for the oxidation 
of tissues and the release of energy. 

Food-taking. — The grasshopper is provided with two pairs 
of jaws, a forklike ventral-lying pair, the maxillce, and a pair of 
hard toothed jaws for cutting, called the man'dihles. These 
parts are covered when not in use by two flaps, the upper and 
lower lips. The leaf upon which the grasshopper feeds is held 
in place in the mouth by means of the little jaws, or maxillae, 
while it is cut into small pieces by the mandibles. 

Blood-making. — Just behind the mouth is a large crop into 
which empty the contents of the salivary glands. It is this fluid 
mixed with digested food that we call the ''grasshopper's 
molasses.'' After the food is digested by the action of the saliva 
and other juices, it passes in a fluid state through the walls of 
the intestine, where it becomes part of the blood. As blood it 
is passed on to tissues, such as muscle, to make new material to 
be used in repairing that \7hich is used up during the flight of 
the insect or to be oxidized to release energy. 

Eyes. — Examination of the compound eye with a lens shows 
the whole surface to be composed of tiny hexagonal spaces called 
facets (f assets). Each facet marks the surface of a unit {om- 
matid'ium) of the compound eye. The separate units of the 
compound eye probably each give a separate impression of light 
and color. Thus a compound eye is most favorable for per- 
ceiving the movement of objects. The grasshopper has three 
simple eyes also on the front of the head. The simple eyes 
probably are able only to perceive light and darkness. 

Other Sense Organs. — The segmented feelers, or antennce, 
have to do with the sense of touch and smell. The eardrum, or 
tym'panum, of the grasshopper is found under the wing on the 



220 



THE INSECTS 




stages in the life history of the grasshopper. 
Note the absence of wings in 1 and 2. The 
adult female 4 is laying eggs in holes she has 
made in the ground. 



first segment of the abdomen. Covering the body and on the 
appendages, are found hairs (sensory hairs) which appear to 
make the insect sensitive to touch. Thus the armor-covered 

animal is in touch with 
its surroundings. 

Nervous System. — 
The nerve chain, as in 
the crayfish, is on the 
ventral side of the body. 
It passes around the 
gullet near the head to 
the dorsal side, where a 
collection of ganglia 
forms the brain. Nerves 
leave the central system 
as outgoing fibers which 
bear motor impulses. 
Other nerve fibers pass 
inward, and produce sensations. These are called sensory fibers. 
Life History. — The female grasshopper lays her eggs in a 
hole which she has dug in the ground with her ovipositor. 
From twenty to thirty fertilized eggs are laid in the fall; these 
hatch out in the spring as tiny wingless grasshoppers. The 
young molt in order to grow larger, each grasshopper under- 
going about five molts before reaching the adult state. Since 
no great change in form occurs, the metamorphosis is said to 
be incomplete. In the fall most of the adults die, only a few 
surviving the winter. 

Economic Importance. — Grasshoppers or locusts have done 
great harm since the days of the Pharaohs at least. They eat 
the young leaves of grass, corn, wheat, and other crops, destroy- 
ing promising fields of grain and sometimes leaving desolate 
and barren wastes behind them. Birds and parasites are their 
natural enemies. Plowing the fields after the eggs are laid 
helps to destroy them. 

Relatives of the Locust. — Among the near relatives are the 
brown or black crickets, cockroaches and "waterbugs," the 
katydid, praying mantis, and many others. All of these in- 



THE BUTTERFLY 



221 




on a 



sects have the hind wings^ when present, folded up lengthwise 
against the body when at rest mouth parts fitted for biting, 
and an incomplete metamorphosis. They are placed in an 
order called Orthop'tera because the 
posterior wings are folded straight 
against the sides of the body when at 
rest (orthos, straight, pteron, wing). 

The Butterfly. — The body of the 
butterfly, as that of the grasshopper, 
is composed of three regions. The 
legs of the butterfly are relatively 
smaller and weaker than those of 

the grasshopper, while the wings are Scales and scale sockets 

relatively larger in the first-named butterfly's wing, 

insect. Under the microscope the 

wing is seen to be covered with thousands of Httle colored 
scales^ each of which fits into a socket in the membranous 
wing. These scales cause the name Lepidop'tera (lepis. scale, 
pteron, wing) to be given to this order of insects. The long pro- 
boscis, a sucking tube through which the insect sucks nectar 

from the flowers, is another characteristic 
by which the Lepidoptera may be known. 
Life History of the Cabbage Butterfly. — • 
Although a frequent visitor of our gardens, 
the cabbage butterfly is perhaps less famil- 
iar than the earlier stage in which it ap- 
pears as a long green worm which eats the 
cabbage leaves. 
Egg. — The eggs are laid in the early 
. , „ , , , spring on the leaves of young cabbage 

A butterfly's head: , , n^, n i n i 

A, antenna; E, com- plants. They are small, pale yeUow, and 
pound eye; L.P. labial dehcately marked with fine hues. You 

palpus;- Pr., proboscis. . i i r ^^ j. n t .-i 

have to look careiully to find them. 
Larva, — In about a week the egg hatches and a tiny green 
worm or larva crawls out. It has a long segmented body, three 
pairs of small true legs on the first three segments of the body, 
and five pairs of prolegs or caterpillar legs farther back, which 
are of great assistance in holding on to a leaf. The mouth is 




222 



THE INSECTS 



provided with toothed mandibles for cutting the leaves. The 
larva eats ravenously and grows rapidly. 

Pupa. — After two weeks of active life, the pupa, a resting 
stage, is formed. The larva fastens itself to a cabbage leaf, 
fence rail, or some other convenient object, and molts. As the 
skin slips off, the pupa — in this case called a chrysalis (kris'a-lis) 
— appears. It is a smaU oval object, usually green, but some- 
times varying a Httle to 
harmonize with its sur- 
roundings. This stage re- 
mains for two weeks in 
summer and longer in cold 
weather. It then cracks 
open down the back and 
the butterfly comes out. 

Adult. — The butterfly 
has two pairs of large, 
strong, white or pale yel- 
low wings with two or three 
black spots on them. The 
legs are short and weak, 
the antennae are slender 
and knobbed, and the suck- 
ing proboscis is coiled Hke 
a tiny watch spring on the 
ventral side of the head. 
A Complete Metamorphosis is shown by this insect, which 
during its development passes through four distinct stages — 
the egg, larva, pupa, and adult. 

Economic Importance and Control. — The harm is done by the 
larva, which riddles the cabbage leaves by means of its sharp, 
pointed mandibles. Spray the plants with a solution of arsenate 
of lead or Paris green as soon as the larvae are seen. 

The Moth. — The big electric-light moth, cecropia, is an insect familiar 
to most of us. In general it resembles a butterfly in structure. Several 
differences, however, occur. The body is much stouter than that of a 
butterfly. The wings and body appear to have a thicker coating of hairs 
and scales, and the antennae are feathery. The position of the wings 




Life history of the cabbage butterfly: A 
adult; B, two views of egg, much magnified; 
C, larva; D, chrysalis. 



THE MOTH 



223 



when at rest forms another easy way of distinguishing the one insect 
from the other; the butterfly's wings are then held vertical, while a moth's 
are spread out horizontally or are folded over the body. 

Development. The Egg. — The eggs, cream-colored and as large as a 
pinhead, are deposited in small 
clusters on the under side of 
leaves of the food plant. 

The LarvcE are at first tiny 
black caterpillars, which later 
change to a bluish green color 
with projections of blue, yellow, 
and red along the dorsal side. 

The Pupal Stage. — Unlike 
the butterfly, the moth passes 
the quiescent stage in a case 
which the larva has spun, 
called a cocoon. The cocoon of 
the cecropia may be found in 
the fall on willows or alders. 

If the cocoon is cut open 
lengthwise (see Figure), the 
dormant insect or pupa will be 
found together with the cast- 
off skin of the caterpillar 
which spun the case. 

Silkworms. — The American 
silkworm is another well- 
known moth. The cocoons, 
made in part out of the leaves 




Life history of the cecropia moth. Above, 
the adult; the larva (caterpillar) in center; 
the pupal case to right, below; the same cut 
open at left, below. From photograph loaned 
by the American Museum of Natural History. 



of the elm, oak, or maple, fall to the ground when the leaves drop, and hence 
are not so easily found as those of the cecropia. This moth is a near relative 
of the Chinese silkworm, and its silk might be used with success were it not 
for the high rate of labor in this country. The Chinese silkworm (p. 4) is 
raised with ease in southern California. China, Japan, Italy, and France, 
because of cheap labor, are still the most successful silk-raising countries. 



Differences Between Moths and Butterflies 
Butterfly Moth 



Antennae threadlike, usually 

knobbed at tip. 
Fly in daytime. 
Wings held vertically when at 

rest. 
Pupa naked. 



Antennae feathery or threadlike, 

never knobbed. 
Usually fly at night. 
Wings held horizontally or folded 

over the body when at rest. 
Pupa usually covered by a cocoon. 



224 



THE INSECTS 




Complete metamorphosis of the house fly 
the four stages in its life history. 



Moths and butterflies are both characterized by having a sucking pro- 
boscis, membranous wings covered with scales, and by imdergoing a com- 
plete metamorphosis or change of form. By these characteristics we know 
them to be members of the order Lepidoptera. 

Diptera. The Typhoid 
Fly. — This name was given 
to the common house fly 
by L. O. Howard, the Chief 
of the Bureau of Ento- 
mology, United States 
Department of Agriculture; 

we shall see later with what reason. The body of the fly, as 

of other insects, has three divisions. The membranous wings 

appear to be two in number, a second pair being reduced to 

tiny knobbed hairs called balancers. The function of the 

balancers is apparently that 

of equiUbrium. 
Head. • — The head is 

freely movable, and the 

compound eyes are ex- 
tremely large. Seemingly 

the fly has fairly acute 

vision. Home experiments 

can be easily made which 

prove its keenness of scent 

and taste. It is well 

equipped to care for itself 

in its artificial environment 

in the house. 
Mouth Parts. — The 



C/aiv from tip of foot 

MAQNiriED 1500 DIAMETERS 

\Typhoid Bacilli 



Lowe, 

Joints of 

Foot 

MAGNIFIED 
150 DIAMETERS 




^^^^^ i( 



Foot of a house fly, highly magnified 



mouth parts of the fly are prolonged to form a proboscis, which 
is tonguelike, the animal obtaining its food by lapping and suck- 
ing. It is the rubbing of this file-like organ over the surface of 
the skin that causes the painful bite of the horsefly. 

Foot. — If possible, we should examine the foot of a fly under 
the compound microscope. The foot shows a wonderful adapta- 
tion for clinging to smooth surfaces. Two or three pads, each 
of which bears tubelike hairs that secrete a sticky fluid, are found 



THE TYPHOID FLY 



225 



on its under surface. It is by this means that the fly is able to 
walk upside down. Hooks are also present which doubtless aid 
in locomotion in this position. 

Development. — The development of the typhoid fly is 
extremely rapid. A female 
may lay from one hundred 
to two hundred eggs. These 
are usually deposited in filth 
or manure. Dung heaps 
about stables, ash heaps, 
garbage cans, and fermenting 
vegetable refuse form the best 
breeding places for flies. In 
warm weather, within a day 
after the eggs are laid, the 
young maggots, as the larvae 
are called, hatch. After about 
one week of active feeding, 
these wormHke maggots be- 
come quiet and go into the 
pupal stage, whence under favorable conditions they emerge 
within less than another week as adult flies. The adults breed 
at once, and in a short summer there may be over ten genera- 




Showing how flies may spread disease by 
means of contaminating food. 




When flies are plentiful, there is a considerable increase in 
the number of cases of illness among babies. 

tions of flies. This accounts for the great number. Fortunately 
few flies survive the winter. 

The Typhoid Fly a Pest. — The common fly is recognized as a 
pest the world over. Flies have long been known to spoil food 
through their filthy habits, but it is more recently that the very 



226 THE INSECTS 

serious charge of spreading diseases, caused by bacteria, has been 
laid at their door. The foot of the fly, covered with hair and 
a sticky fluid, is adapted to carry a great many bacteria. In a 
recent experiment it was found that a single fly might carry 
anywhere from 500 to 6,600,000 bacteria, the average number 
being over 1,200,000. Not all of these are harmful, but they 
might easily include those of typhoid fever, tuberculosis, sum- 
mer complaint, and possibly other diseases. The rapid increase 
of flies during the summer months has a definite relation to 
the increase in the number of cases of summer complaint and 
probably also of typhoid. It has been estimated that the loss 
caused from typhoid is in a single year $350,000,000 in the 
United States alone. A large part of this loss is indirectly due 
to the typhoid fly. 

Control. — • All windows should be screened during the summer 
months and food kept away from flies. FHes should be caught 
in traps or on sticky fly paper. In order to destroy breeding 
places, all manure and refuse should be removed at least once 
a week. 

Other Diptera. — Other examples of the Dip^tera group are 
the mosquitoes, of which more wiU be said hereafter; the 
Hessian fly, the larvae of which feed on young wheat; the botfly, 
which in a larval state is a parasite in horses; the dreaded 
tsetse fly of South Africa, which causes disease in horses and 
cattle by means of the transference of a parasitic protozoan, 
much like that which causes malaria in man; and many others. 

Among the few flies useful to man may be mentioned the 
tachina flies, the larvae of which feed on the cutworm, the army 
worm, and various other kinds of injurious caterpillars. 

Characteristics of Diptera. — Members of this group have only 
one pair of wings; the mouth parts are fitted for sucking, rasping, 
or piercing, and they pass through a complete metamorphosis. 

Coleop'tera: Beetles. — Beetles are the most widely distributed and 
among the most numerous of all insects. There are over one hundred 
thousand living species. 

Any beetle will show the following characteristics: (1) The body is 
usually heavy and broad. Its exoskeleton is hard and tough, this chitinous 
body covering being better developed in the beetles than in any other of 



BEETLES, BUGS 



227 



the insects. (2) The three pairs of legs are stout and rather short. 

(3) The outer wings are hard and fit over the under wings Uke a shield. 

(4) The mouth parts, provided with an upper and lower hp, are fitted for 
biting. They consist of very heavy curved pincher-shaped mandibles, which 
are provided with palps. 

The Life History of a Beetle. — The June beetle (May beetle) and po- 
tato beetle are excellent examples. May beetles lay their eggs in the 
ground, where they hatch into 
cream-colored grubs. A grub 
differs from the maggot or larva 
of the fly in possessing three pairs 
of legs. These grubs hve in bur- 
rows in the ground, where they 
feed on the roots of grass and 
garden plants. The larval form 
remains underground from two 
to three years, the latter part 
of this time as an inactive 
pupa. During the latter stage 
it lies dormant in an ovoid area 
excavated by it. Eventually the 
wings (which are budlike in the 
pupa) grow larger, and the adult 
beetle emerges fitted for its Hfe 
in the open air. 

Order Hemip'tera: Bugs. — 
The cicada, or, as it is incorrectly 
called, the locust, is a famihar 
insect to all. Its droning song, 
one of the accompaniments of 
a hot day, is produced by a 
drumlike organ which can be 
found just behind the last pair of 
legs. The sound is caused by a 
rapid vibration of the tightly 

stretched drumhead. The body is heavy and bulky. The wings, four in 
number, are relatively small, but the powerful muscles give them very rapid 
movement. The anterior wings are larger than the posterior. The legs 
are not large or strong, the movement when crawling being sluggish. One 
of the characteristics of the cicada, and of all other bugs, is that the mouth 
parts are prolonged into a beak with which the animal first makes a hole 
and then sucks up the juices of the plants on which it lives. 

Life History. — The seventeen-year cicada laj^s her eggs in twigs of 
trees, and in doing this causes the death of the twig. The young leave 
the tree immediately after hatching, burrow underground, and pass from 




•■^'v-.""" ' 



:;ffili*iiil 



■■-■•-■•••••■%>,;, 



The potato beetle: eggs, larvae, pupa, 
and adults. 



228 



THE INSECTS 



thirteen to seventeen years there, depending upon the species of cicada. 
They live by sucking the juices from roots. During this stage thej' some- 
what resemble the grub of the beetle (June bug) in habits and appearance. 
When they are about to molt into an adult, they climb above ground, 
cling to the bark of trees, and then crawl out of the skin as adults. 




Cicada with wings spread, showing abdo- 
men Ab, head H, thorax Th: also ventral 
view, showing beak B, and eye E. Below is 
seen a pupal case with split down the back. 



Aphids. — The aphids are among the most interesting of the bugs. 
They are familiar to all as tinj^ green Hce seen swarming on the stems and 
leaves of the rose and other cultivated plants. They suck the juices from 
stem and leaf. Plant lice have a remarkable hfe history. Early in the 
year eggs develop into wingless females, which produce U\'ing young, all 
females. These in turn reproduce in a similar manner, until the plant on 
which they Hve becomes overcrowded and the food supply runs short. 
Then a generation of winged aphids is produced. These fly awaj^ to other 
plants, and reproduction goes on as before until the approach of cold 
weather, when males and females appear. Fertilized eggs are then pro- 
duced which give rise to 3'oung the following season. 

The aphids exude from the surface of the body a sweet fluid called 
honeydew. This is given off in such abundance that it is estimated if 
an aphid were the size of a cow, it would give two thousand quarts a day. 
This honeydew is greatlj^ esteemed by other insects, especially the ants. 
For the purpose of obtaining it, some ants care for the aphids, even pro- 
viding food and shelter for them. In return the aphid, stimulated b}' a 
stroking movement of the antenna of the ant, gives up the honeydew to 
its protector. (See Figure, page 241.) 

Neurop'tera. — The dragon fly receives its name because it preys on 
insects. It eats, when an adult, mosquitoes and other insects which it 
captures while on the wing. Its four large lacelike wings give it power of 
very rapid flight, while its long narrow body is admirably adapted for the 
same purpose. The large compound eyes placed at the sides of the head 
give keen sight. It possesses powerful jaws (almost covered by the upper 
and lower lips). 




NEUROPTERA, HYMENOPTERA 229 

The long, thin abdomen does not contain a sting, contrary to the belief 
of most children. These insects deposit their eggs in the water, and the 
fact that they may be often seen with the end of the abdomen curved 
down under the surface of the water in the act of depositing the eggs has 
given rise to the behef that they were then engaged in stinging something. 
The egg hatches into a form of larva called a nymph, which in the dragon 
fly is characterized by a greatly developed lower Up. When the animal is 
a;t rest, the lower hp covers the large biting jaws, which can be extended 
so as to grasp and hold its prey. 
The nymphs of the dragon fly 
take oxygen out of the water by 
• means of gill-Hke structures 
placed in the posterior part of 
the food tube. They may Uve 
as larvae from one summer to as 
long as two years in the water. 
They then crawl out on a stick, 
molt by sphtting the skin down 
the back, and come out as adults. 

A nearly related form is the Dragon fly: notice the long abdomen 
damsel fly. This may be distin- and large compound eyes, 

gmshed from the dragon fly by 

the fact that when at rest the wings are carried close to the abdomen, 
while in the dragon fly they are held in a horizontal position. 

May Flies. — Another near relative of the dragon fly is the May fly. 
These insects in the adult stage have lost the power to take food. Most 
of their life is passed in the larval stage in the water. The adults some- 
times Ave only a few hours, just long enough to mate and deposit their 
eggs. 

Hymenop'tera. — We have already learned something of the structure 
of the bee, an example of this order. Other relatives are the wasps, ich- 
neumons (wasp-like insects with long ovipositors), and the ants. The 
structural characteristics of this group are two pairs of membranous wings, 
and mouth parts fitted for biting and lapping. They all undergo a com- 
plete metamorphosis, the young being helpless wingless creatures somewhat 
like the maggots of the fly. Of this group we shall learn more later. 

Characteristics of Insects. — The orders of insects mentioned 
above are only a few examples of this very large group. In all of 
the above forms we have seen certain likenesses and certain 
differences in structure, but all of the above have had three 
body divisions, three pairs of legs, and have possessed in the 
adult stage air tubes called trachese. These are the principal 
characteristics by which we may identify the insects. 



230 



SPIDERS AND MYRIAPODS 



Spiders and Myriapods. — Spiders, millepedes, and centipedes are not true 
insects, although they are nearly alUed to them. 

The body of a spider, like that of the higher crustaceans, has onl}- two 
di^dsionsJ cephalo thorax and abdomen; four pairs of walking legs mark 
another difference from insects. Wings are alwaj^s lacking. Spiders usually 
have four pairs of simple ej'es and breathe by means of lunglike sacs in 

the abdomen, the openings of which 
can sometimes be seen just behind 
the most posterior pair of legs. 
Another organ possessed by the 
spider, which insects do not have 
(except in a larval form), is kno"WTi 
as the spinneret. This is a set of 
glands which secrete in a liquid 
form the silk which the spider 
spins. On exposure to air, tliis 
fluid hardens and forms a very 
tough building material which com- 
bines lightness with strength. 

Uses and Form of the Web. — 
The web-making instinct of spiders 
forms an interesting study. Our 
common spiders may be grouped 
according to the kind of web they 
spin. The web in some cases is 
used as a home; m others it 
forms a snare or trap. Occasionally 
the web is used for ballooning, 
spiders having been noticed cling- 
ing to their webs miles out at 
sea. The webs seen most fre- 
quently are the so-called cobwebs. These usually serve as a snare rather 
than a home, some species remaining away from the web most of the time. 
Other webs are funnel-shaped, still others are of geometrical exactness, while 
one form of .spider makes its home underground, lines the hole with silk, 
and makers a trapdoor which can be closed after the spider has retreated to 

its lair. 

Myriapods. — We are all famihar with the harmless and common 
thousand legs found under stones and logs. It is a representative of the 
group of animals known as the millepedes. These animals have the body 
diN-ided into two regions, head and trunk, and have two pairs of legs for 
each body segment. The centipedes, on the other hand, have only one 
pair of legs to each segment. Both are representatives «^f the cla,?s Myri- 
ap'odo. None of the forms in the eastern part of the United States are 
poisonouK. 




Tarantula, a spider, about one third 
actual size. The palpi and the four pairs 
of legs are attached to the cephalothorax; 
the spinnerets are at the end of the 
abdomen, below. Photograph from 
American Museum of Natural Histor3\ 



INSECTS AXD CRUSTACEANS C0:MPARED 231 

Insects and Crustaceans Compared. — Both crustaceans and 
insects belong to a large group of animals which agree in that 
they have jointed appendages and bodies, and that they pos- 
sess an exoskeleton. This group or phylum is known as the 
Arthrop'oda. Spiders and myriapods are also included in this 
group. 

Insects differ structurally from crustaceans in ha^dng three 
regions in the body instead of two. The number of legs (three 
pairs) is definite in the insects; in the crustaceans the number 




A poisonous centipede frora Texas. Half natural size, 
photograph by Davison. 



Fiom 



sometimes varies, but is always more than three pairs. The- 
exoskeleton, composed wholly of chitin in the insects, is usually 
strengthened with lime in the crustaceans. Both groups have 
compound eyes, but those of the Crustacea are stalked and 
movable. The other sense organs do not differ greatly. The 
most marked differences are physiological. The crustaceans 
take in oxygen from the water by means of gills, while the 
insects are air breathers, using for this purpose air tubes called 
trachece. 

Both insects and crustaceans, because of their exoskeleton, 
must molt in order to increase in bulk. 



Classification of Arthropoda 

Phylum Arthropoda 

Class, Crusta'cea. Arthropods with Km}' and chitinous exoskeleton, rarely 
more than 20 body segments, usually breathing by gills, and having 
two pairs of antennae. 



232 THE INSECTS 

Subclass I. Entomos'traca. Crustacea with a variable number of seg- 
ments, chiefly small forms with simple appendages. Some degenerate 
or parasitic. Examples: barnacles, water flea (Daphnia), and co'pepod 
{Cy' clops) . 

Subclass II. Malacos'traca. Usually large Crustacea having nineteen 
pairs of appendages. Examples: American lobster {Hom'arus ameri* 
ca'nus), crab {Cancer), and shrimp {Palcemon'etes). 
Class, Hexap'oda or Insecta (insects). Arthropoda having chitinous exo- 
skeleton, breathing by air tubes (trachece), and having three distinct 
body regions. 

Order, Ap'tera (without wings). Several wingless forms. Example: 
springtails. 

Order, Orthoptera (straight wings). Example: Rocky Mountain locust. 

Order, Lepidoptera (scale wings). Examples: cabbage butterfly, cecropia 
moth. 

Order, Diptera (two wings). Examples: fly, mosquito. 

Order, Hemiptera (half wing). Examples: all true bugs, plant lice, and 
cicada. 

Order, Neuroptera (nerve wings). Examples: May fly, dragon fly. 

Order, Coleoptera (shield wings). Example: beetles. 

Order, Hymenoptera (membrane wings). Examples: bees, wasps, ants. 
Class, Arachnida (a-rS,k'nI-da) . Arthropoda with head and thorax fused. 
Six pairs of appendages. No antennae. Breathing by lung sacs (spi- 
ders) or tracheae. Examples: spiders and scorpions. 
Class, Myriapoda. Arthropoda having long bodies with many segments; 
one or two pairs of appendages to each segment. Breathing by means 
of tracheae. Example: centipede. 

An exercise for field work with a simple key for identification of orders 
will be found in Sharpe's Laboratory Manual, Prob. XXX. 

Summary. — This chapter has attempted to have you build 
up your own definition of what an insect is by comparing a 
number of orders to see what characteristics they have in 
common. You have found them to have a segmented body, 
with three divisions, head, thorax, and abdomen, three pairs 
of jointed legs, a chitinous body covering, compound and 
usually simple eyes, breathing through air tubes (tracheae), and 
undergoing a metamorphosis. 

Problem Questions. — 1. Give ten good reasons why insects 
are so numerous. 

2. Give briefly the characteristics of the Orthoptera, Lepi- 
doptera, Diptera, Hymenoptera. 



CLASSIFICATION OF ARTHROPODA 233 

3. How do insects and crustaceans differ? 

4. Make a table classifying the Arthropoda. 

» 

Problem and Project References 

Cockerell, Zoology. World Book Company. 

Comstock, Insect Life. D. Appleion and Company. 

Comstock, An Introduction to Entomology. Comstock Publishing Company 

Hegner, College Zoology. The Macmillan Company. 

Hodge, Nature Study and Life. Ginn and Company. 

Howard, The Insect Book. Doubleday, Page and Company. 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Kellogg, American Insects. Henry Holt and Company. 

Needham, Outdoor Studies. American Book Company. 

Sharps, Laboratory Manual. American Book Company. 



XX. GENERAL CONSIDERATIONS FROM THE 
STUDY OF INSECTS 

Problem, To determine how insects have become winners in 



lifers race by means of — 

(a) Protective resemblance, 

(b) Aggressive resemblance, 

(c) Mimicry. 
(Laboratory Manual, Prob. 

Probs. U, 15.) 



id) Communal life, 
(e) Symbiosis. 
(/) Parasitism. 
XXXI; Laboratory Problems^ 



Insects are by far the most numerous of all animals. It is 
estimated that there are more species of insects than of all other 

kinds of animals upon the globe. Why 
should insects have developed in so 
much greater numbers than other 
animals ? We cannot explain this, but 
some light is thrown on the problem 
when we consider some of the ways in 
which insects have become winners in 
life's race. 

Protective Resemblance. — When 
we remember that the chief enemies 
of insects are birds and other animals 
which use them as food, we can see 
that the insect's power of rapid flight 
must have been of considerable im- 
portance in escaping from enemies. 
But other means of protection are 
seen when we examine insects in their 
native haunts. We have noted that 
various animals, such as the earth- 
worm and crayfish, escape observation 
because they have the color of their 
234 




Three walking sticks on a 
twig, showing protective re- 
semblance. 



RESEMBLANCE 



235 



surroundings. Insects give many interesting examples of pro- 
tective coloration or protective resemblance. The grasshopper 
is colored like the grass on which it lives. The katydid, with its 
green body and wings, can scarcely be distinguished from the 
leaves on which it rests. The walking stick, which resembles the 
twigs on which it is found, and the walking-leaf insect of the 
tropics, are other examples. 

One example frequently described is the dead-leaf butterfly of 
India. This insect at rest resembles a dead leaf attached to a limb; 
in flight it is conspicuous, because of its 
vivid colors. The underwing moth is 
another example of a wonderful simu- 
lation of the background of bark on 
which the animal rests in the daytime. 
At night the brightly colored under- 
wings perhaps give a signal to others 
of the same species. The beautiful 
luna moth, in color a delicate green, 
rests by day among the leaves of the 
hickory. When frightened, measur- 
ing worms stand out stiff upon the 
branches on which they crawl, thus 
simulating lateral twigs. Hundreds 
of other examples might be given. 

This likeness of an animal to its 
immediate surroundings has already 
been noted as protective resemblance. 

Aggressive Resemblance. — Some- 
times animals which resemble their 
surroundings are thus better able to 
catch their prey; they show aggresive 
resemblance. The polar bear is a 

notable example. The mantis has strongly built fore legs, 
with which it seizes and holds insects on which it preys. It 
has the color of its immediate surroundings, and is thus enabled 
to seize its prey before the latter is aware of its presence. 
Many other examples could be given. 

Warning Coloration and Protective Mimicry, — Some insects are 




Underwing moth: above, in 
flight; below, at rest on bark. 



236 INSECTS — GENERAL CONSIDERATIONS 



extremely unpleasant, either to smell or to taste, while others are 
pro^dded with means of defense such as poison hairs or stings. 
Those animals which are harmful and brightly colored or marked 
as if to warn animals to keep off or to take the consequences, 
show warning coloration. Examples of insects which show warn- 
ing by color may be seen in many examples of beetles, espe- 
cially the spotted ladybirds, potato beetles, and the hke. 

Wasps show 3^ellow bands, while 
many forms of caterpillars are 
conspicuous^ marked or colored. 
Some insects, especially cater- 
pillars, wliich are harmless, are 
brightly colored and protrude 
horns, or pretend to sting when 
threatened with attack. These 
animals evidently mimic animals 
which really are protected by a 
sting or by poison, although this 
is not voluntary on the part of 
the insect. When a harmless 
insect resembles a harmful insect 
we call it mimicry. 

One of the best-known exam- 
ples of insect mimicry is seen in 
the imitation of the monarch 
butterfly by the viceroy. The 
monarch butterfly {Anosia plexippus) is an example of a race 
which has received protection from enemies in the struggle for 
hfe, because of its nauseous taste, and, perhaps, because its 
caterpillar feeds on plants of no commercial value. Another 
butterfly, less favored by nature, resembles the monarch in out- 
ward appearance. This is the viceroy. It seems probable that 
in the early history of this edible species some of them escaped 
from the birds because they resembled in both color and form the 
species of inedible monarchs. So for generation after generation 
the ones which were most like the inedible species lived and 
produced new offspring, the others becoming the food of birds. 
Ultimately a species of butterflies was formed that owed its 




Monarch and ^'ice^oy butterflies: 
the viceroy (below) shows protective 
mimicry. 



OTHER MEANS OF PROTECTION 



237 





existence to the fact that it resembled another more favored 
species. This is one of the ways in which nature selects the 
animals which exist upon the earth. Many other examples of 
mimicry may be found among 
insects. Some harmless flies 
imitate bees, which sting, as 
shown in the figure. 

Other means of Protection. — 
The chief insect enemies are 
the birds, and from these 
the most effective protection 
seems to be hairs on the body. 
Few birds eat hairy cater- 
pillars of any species; fortu- 
nately, however, the hairy 
larvae of the gypsy moth, a 
serious pest, are eaten by no 
less than thirty-one species 
of birds. The odors or ill 
flavors of insects seem to 
be generally protective, but 
stinging insects do not appear 
to be protected from all birds, flycatchers and swallows habitu- 
ally feeding on the bees and wasps. There is a growing 
tendency among zoologists to place less emphasis on these 
adaptations as a means of preserving species. 

Communal Life among Insects. — Insects are of special in- 
terest to man because among certain species a system of social 
life has arisen comparable to that which exists among men. In 
connection with this communal life, nature has worked out a 
division of labor which is very remarkable. This can be seen 
in tracing out the lives of several of the insects which live in 
communities. 

Solitary Wasps. — Some bees and wasps lead a solitary existence. 
The solitary and digger wasps do not live in communities. Each female 
constructs a burrow in which she lays eggs and rears her young. The 
young are fed upon spiders and insects previously caught and then stung 
into insensibility. The nest is closed up after food is supplied, and the 



Supposed cases of mimicry: 1, a bum- 
blebee, mimicked by 2, a kind of fly; 3, 
a wasp, mimicked by 4, another kind of 
fly. The bumblebee and wasp are of the 
order Hymenoptera; the mimics, of the 
order Diptera. 



238 



INSECTS — GENERAL CONSIDERATIONS 



young later gnaw their way out. In the life history of such an insect there 
is no communal life. 

Bumblebee. — In the life history of the big bumblebee we see the be- 
ginning of the community instinct. Some of the female bees (known as 
queens) survive the winter and lay their eggs the following spring in 
a mass of pollen, which they have previously gathered and placed in a 
hole in the ground. The young hatch as larvae, then pupate, and finally 

become workers, or imperfect 
females in which the egg-laying 
apparatus, or ovipositor, is 
modified to be used as a sting. 
The workers bring lq pollen to 
the queen, in which she lays 
more eggs. Several broods of 
workers are thus hatched during 
a summer. In the early fall a 
brood of males or drones, and 
egg-laying females or queens, 
are produced instead of workers. 
By means of these egg-producing 
females the brood is started the 
following year. 

The Honeybee. — The 
most wonderful communal 
life has been developed 
among the honeybees.^ 

The honeybee in a wild 
state makes its home in a 
hollow tree; hence the term 
'^ bee tree . " In the hive the 
colony usually consists of a 
A, worker; B, queen; queen, or egg-laying female, 




The honeybee 
C, male (drone), 
hind leg, as seen from the 
behind: 4, femur; 1, 5, tibia; 2, 7, meta 
tarsus; 3, 8, foot; 6, wax shears. 



Above is shown aj^orker^ ^ ^^^ hundred drones, or 



males, and several thou- 
sand imperfect females, or 



* Their daily life may be easily watched in the schoolroom, by means of one 
of the many good and cheap observation hives now made to be placed in a 
window frame. Directions for making a small observation hive for school work 
can be found in Hodge, Nature Study and Life, Chapter XIV. Bulletin No. 1, 
U.S. Department of Agriculture, entitled The Honey Bee, by Frank Benton, is 
valuable for the amateur beekeeper. Farmers' Bulletin 447 on Bees, by E. F. 
Phillips, is also most useful. 



COMMUNAL LIFE 



239 



workers. The colonies vary greatly in numbers, in a wild state 
there being fewer in the colony. The division of labor is well 
seen in a hive in which the bees have been hving for some 
weeks. The queen does nothing except lay eggs, sometimes lay- 
ing three thousand eggs a day and keeping this up, during the 
warm weather, for several years. She may lay a million eggs 
during her hfe. She does not, as is popularly beheved, rule the 
hive, but is on the contrary a captive most of her life. Most 
of the eggs are fertilized by the sperm cells of a male; the un- 
fertilized eggs develop into 
males or drones. After a 
short existence in the hive 
the drones are usually driven 
out by the workers. The 
fertilized eggs may develop 
into workers, but if the 
young larva is fed with a 
certain kind of food, it will 
develop into a young queen. 
The cells of the comb are 
built by the workers out of 
wax secreted from the under 
surface of their bodies. The 
wax is cut off in thin plates 
by means of the wax shears 
between the two last joints 
of the hind legs. These cells 
are used by the queen to 
place her eggs in, one to each 

cell, and the young are hatched after three days, to begin life as 
footless white grubs. For a few days they are fed on partly 
digested food called bee jelly, regurgitated from the stomach 
of the workers. Later they receive pollen and honey to eat. 
A Httle of this mixture, known as bee bread, is put into the 
cells, and the lids covered with wax by the working bees, and 
the young larvae allowed to pupate. After about two weeks of 
quiescence in the pupal state, the adult worker breaks out of the 
cell and takes her place in the hive, first caring for the young 




Hornets' nest, open to show the cells 
of the comb. Photograph by Overton. 



240 INSECTS — GENERAL CONSIDERATIONS 

as a nurse, later making excursions to the open air after food 
as an adult worker. 

If a new queen is to be produced, several of the cell walls are 
broken down by the workers, making a large ovoid ceU in which 
one egg is left. The young bee in this cell is fed during 
its whole larval life upon bee jelly, and grows into a queen of 
much larger size than an ordinary worker. When a young queen 
appears, great excitement pervades the community; the bees 
appear to take sides; some remain with the young queen in 
the hive, while others follow the old queen out into the world. 
This is called swarming. They usually settle around the queen, 
often hanging to the limb of a tree. While the bees are swarm- 
ing, certain of the workers, acting as scouts, determine on a site 
for their new home; and, if undisturbed, the bees soon go there 
and construct their new hive. This instinct is of vital impor- 
tance to the bees, as it provides them with a means of forming 
a new colony. A swarm of domesticated bees may be quickly 
hived in new quarters. 

We have already seen (pages 31 and 32) that the honey- 
bee gathers nectar; this is swallowed and kept in the crop until 
after the return to the hive, where it is regurgitated into cells 
of the comb. It is now thinner than what we call honey. 
To thicken it, the bees swarm over the open cells, moving their 
wings very rapidly, thus evaporating some of the water in the 
honey. A hive of bees has been known to make over thirty- 
one pounds of honey in a single day, although the average 
record is very much less than this. 

Ants. -^ Ants are the most truly communal of all the insects. Their life 
history and habits are not so well known as those of the bee, but what is 
known shows even more wonderful specialization. The inhabitants of a 
nest may consist of wingless workers, which in some cases may be of two 
kinds, and winged males and females. 

Ant larvse are called grubs. They are absolutely helpless and are taken 
care of by nurses. The pupae may often be seen as they are taken out in 
the mouths of the nurse ants for sun and air. They are wrongly called 
ants' eggs in this stage. 

The nest of a colony consists of underground galleries with enlarged store- 
rooms, nurseries, etc. The ants are especially fond of honeydew secreted 
by the aphids, or plant lice. Some species of ants provide elaborate stables 



SYMBIOSIS 



241 



for the aphids, commonly called ants' cows, supplying them with food and 
shelter and taking the honeydew as their reward. This they obtain by 
licking it from the bodies of the aphids. A Western form of ant, found in 
New Mexico and Arizona, rears a scale 
insect on the roots of the cactus for the 
same purpose. 

It is probable that some species of 
ants are among the most warlike of 
any insects. In the case of the robber 
ants, which live entirely by war and 
pillage, the workers have become 
modified in structure, and can no 
longer work, but only fight. Some 
species go further and make slaves of 
the ants preyed upon. These slaves 
do all the work for their captors, 
even to making additions to their nest 
and acting as nurses to their young. 

The entire communal life of the 
ants seems to be based upon the per- 
ception of odor. If an ant be put into 
a colony to which it does not belong, 
although one of the same species, it 
will be set upon and either driven out 
or killed. Ants never really lose their community odor; those absent for 
a long time, on returning, will be easily distinguished by their odor, and 
eagerly welcomed by the members of the nest. The communication of ants 
as seen when they stop each other, away from the nest, is evidently a 
process of smelling, for they caress each other with the antennae, the organs 
with which odors are perceived. 




Ants and their "cows 
(aphids). 



Symbiosis. — ^We have already seen that plants and animals 
frequently live in a state of partnership or relation of mutual 
help. Such a state is known as a symbiotic relation. The keep- 
ing of the aphids by the ants which use them as /' cows '' is an 
example of this relation among two species of insects. The ants 
provide protection and sometimes food; the aphids give up the 
honeydew of which the ants are so fond. 

But a wider symbiotic relation exists directly between the 
flowering plants and the insects. We all know the very great 
service done the plants by the pollination of the flowers by the 
insects, and we know that the return is the supply of pollen and 
nectar as food for the insects. 



242 



INSECTS — GENERAL CONSIDERATIONS 



Parasitism. — One of the near relatives of the bee called the 
ichneumon (ik-nti'mon) fly does man indirectly considerable 

good because of its habit of 



laying its eggs and leaving its 
young to develop in the bodies 
of caterpillars which are harm- 
ful to vegetation. As this is 
death for the caterpillar, it 
is safe to say that by the 
above means the ichneumons 
save millions of dollars yearly 
to this country. 

Unfortunately, not all insect 
parasites do good. Animals 
of all kinds, but especially 
birds, are infested with lice 
and fleas. The ticks are well 
known for the harm they do, 
while the larvae of the botflies 
which live in the bodies of 

various mammals, as the horse and sheep and cattle^ are 

insect parasites which do much harm. 

Problem. Some relations of insects to man. (Laboratory Manual, 
Prob. XXXII; Laboratory Problems, Probs. 123 to ISl.) 

(a) With reference to disease. 

(b) With reference to destruction of property, 

(c) With reference to benefit to man. 




Ichneumon fly (Thalessa) boring in 
an ash tree to deposit its eggs in the 
burrow of a horntail larva, a wood 
borer. From photograph, natural size- 
by Davison. 



The Relation of Insects to Mankind. — We already have seen 
this relation is twofold, harmful and beneficial. The harmful 
relation may affect man directly, as when human disease is 
carried by insects, or it may be indirect, as in the case of damage 
to crops, trees, stored food, or clothing. The first relation is 
naturally of more importance, as malaria, an extremely prevalent 
disease in some parts of the world, is carried by mosquitoes, 
and typhoid and other intestinal diseases are often distributed 
by flies. 



DISEASE CARRIERS 



243 




<^. 



<^^ 

<^^> 



The Malarial Mosquito. — Fortunately for mankind, not all 
mosquitoes harbor the small one-celled parasite (a protozoan) 
which causes malaria. The harmless mosquito {culex) may be 
usually distinguished from the mosquito (anopheles) which carries 
malaria by the position of the body and legs when at rest. (See 
Figure.) Culex lays eggs in tiny masses shaped like rafts 
of one hundred or more eggs 
in standing water; thus the 
eggs are distinguished from 
those of anopheles, which 
are not in rafts. In a short 
time enough mosquitoes to 
stock a neighborhood may 
develop in rain barrels, 
gutters, or old cans. The 
larvae are known as wig- 
glers. They appear to 
hang on the surface of the 
water, head down in order to 
breathe through a tube at the 
posterior end of the body, the 
end of which projects a short 
distance above the water. In 
this stage they may be easily 
recognized by their peculiar 
movement when on their way 
to the surface to breathe. The 
fact that both larvae and pupae 
take air from the surface of the water makes it possible to kill 
the mosquitoes during these stages by pouring oil on the surface 
of the water where they breed. The introduction of minnows, 
goldfish, or other small fish which feed upon the larvae in 
the water where the mosquitoes breed will do much in freeing 
a neighborhood from this pest. Draining swamps or low 
lands which hold water after a rain is another method of 
extermination. 

Since the beginning of historical times, malaria has been 
prevalent in regions infested by mosquitoes. The ancient city 




Life history of two mosquitoes — at 
the left, culex; at the right, anopheles. 
Note the four steps of each — eggs, 
larva, pupa, adult. 



244 INSECTS — GENERAL CONSIDERATIONS 

of Rome was so greatl}^ troubled by periodic outbreaks of mala- 
rial fever that a goddess of fever was worshiped in order 
to lessen the severity of what the inhabitants believed to be 
a di^'ine visitation. As recently' as 1900 two doctors hved in 
the most malarious district in the swampy area near Rome, 
drank the water and hved the same life as did the natives; 
only taking the precaution to screen themselves from the 
anopheles mosquito. The}' remained free from malaria. A 
little later came the proof that malaria was carried by anoph- 
eles. Living mosquitoes which had bitten malarial patients 
were shipped to England, and there two Enghsh doctors 
allowed these mosquitoes to bite them. Thej^ came down 
with malaria. These experiments and others have shown the 
world how to combat malaria successfully. 

Yellow Fever and Mosquitoes. — Another disease which has 
been proved to be carried by mosquitoes is j^ellow fever. In the 
yesLT 1878 there were 125,000 cases and 12,000 deaths in the 
United States, mostlj^ in Alabama, Louisiana, and Mississippi. 
Dm'ing the French occupation of the Panama Canal zone the 
work was at a standstill part of the time because of the ravages 
of yeUow fever. 

But to-da}' this is changed, and thanks to the experiments per- 
formed in Cuba in 1900 by the commission headed bj^ Major 
Walter Reed, yellow fever is under almost complete control, both 
here and wherever the mosquito (aedes, formerly called stegomyia) 
which carries yellow fever exists. During the series of experi- 
ments two doctors. Dr. James Carroll and Dr. Jesse W. Lazear, 
allowed themselves to be bitten by aedes mosquitoes which had 
previously bitten j^eUow fever patients. Both had j^ellow fever 
and Dr. Lazear died. Later others were similar 1}^ experimented 
upon with the result that we now know conclusively that 
yellow fever is transmitted only by means of a mosquito. 
Hence it has been possible, by draining, oiling, and screening, 
to make Panama a safer place to hve in than many parts of 
the United States. 

Other Diseases due to Insects. — The bubonic plague, the 
dreaded scourge of the East, is brought to man by fleas. The 
sleeping sickness of Africa has already been mentioned (page 



ECOXO:\IIC LOSSES 245 

179) as carried by the tsetse fly. Several other diseases of man 
and of many other animals, especially cattle, are carried by flies. 
The Texas fever of cattle is carried by a cattle tick, an animal 
closely allied to the insects. 

Economic Loss from Insects. — The money value of crops, 
forest trees, stored foods, and other materials destroyed annually 
by insects is beyond behef. It is estimated that they get one 
tenth of the country's crops, at the lowest estimate a matter of 
some S300;000,000 yearly. 

" A recent estimate by experts put the yearly loss from forest insect 
depredations at not less than $100,000,000. The common schools of the 
countrj^ cost in 1902 the sum of §235,000,000, and all higher institutions 
of learning, cost less than 850,000,000, making the total cost of education 
in the United States considerably less than the farmers lost from insect 
ravages." — Slingerland. 

Jb. 1874-1876 the damage to crops by the Rocky Mountain 
locust has been estimated at $200,000,000. The total value of 
all fann and forest crops, excluding animal products, in New 
York, is perhaps $150,000,000, and the one tenth that the insects 
get is worth S15,000,000. It may seem incredible that it costs 
such a sum to feed Xew York's injurious insects every year, but 
it is an average of $66 for each of the 227,000 farms in the state; 
and there are few farms where the crops are not lessened more 
than this amount by insects. 

Insects which damage Garden and Other Crops. — The grass- 
hoppers have been mentioned as among the most destructive 
of these. The larvae of various butterflies and moths do con- 
siderable haiTQ, especially the "cabbage worm," the various 
caterpillars of the hawk moths which feed on grape and tomato 
vines, the cutwoiTQ, a feeder on the roots of all kinds of garden 
tinck, the corn worm, a pest on corn, cotton, tomatoes, peas, 
and beans. The last damages the cotton crop to the amount 
of several millions of dollars annuaUy. 

Among the beetles which are found in gardens is the potato 
beetle, which destroys the leaves of the potato plant. This 
beetle formerly hved in Colorado upon a wild plant of the same 
family as the potato, and came east upon the introduction of the 



246 INSECTS — GENERAL CONSIDERATIONS 

potato into Colorado, evidently preferring cultivated forms to 
wild forms of this family. The asparagus and cucumber beetles 
are also often in evidence. 

The one beetle doing by far the greatest harm in this country is 
the cotton-boll weevil. Imported from Mexico, since 1892 it has 
spread over most of the cotton-growing states. The beetle lays 
its eggs in the young cotton fruit or boll, the larvae feeding upon 
the substance within the boll. It is estimated that if unchecked 
this pest would destroy yearly one half of the cotton crop, a 
matter of over $300,000,000. Fortunately, the experts of the 
United States Department of Agriculture are at work on the 





Four destructive insects: from left to right, the cotton boll weevil, the 
potato beetle, the squash bug, and the celery caterpillar. 

problem, and, while they have not found any way of exter- 
minating the beetle as yet, it has been shown that, by planting 
more hardy varieties of cotton, the crop matures earlier and 
ripens before the weevils have increased in sufficient numbers to 
destroy the crop (see page 51). 

The bugs are among our destructive insects. The most fa- 
miliar examples of our garden pests are the squash bug; the 
chinch bug, which yearly does damage estimated at $20,000,000, 
by sucking the juice from the leaves of grain; and the plant lice, 
or aphids. Some aphids are extremely destructive to vegetation. 
One, the grape Phylloxe'ra, yearly destroys immense numbers of 
plants in the vineyards of France, Germany, and California. 

The Hessian fly, the larvae of which live on the wheat plant, 
was introduced accidentally by the Hessians in their straw 



DESTRUCTIVE INSECTS 



247 



bedding during the Revolution, and has become one of our most 
serious insect pests. 

Insects which harm Fruit and Forest Trees. — Great damage 
is done annually by the larvai of moths. Massachusetts has 
already spent over $5,000,000 
in trying to exterminate the 
accidentally imported gypsy 
moth. The codHng moth, 
which bores int(3 apples and 
pears, is estimated to ruin 
yearly $3,000,000 worth of 
fruit in New York alone, 
which is only one of the 
important apple regions of the 
United States. The codKng 
moth flits over the fruit 
blossoms and lays an egg here 
and there — one in a blossom. 
The young hatch in a day or 
two and eat their way into 
the ovary, where they feed 
and grow with the fruit. 
The fruit ripens early and 
often falls to the ground 
before the perfect fruit is 
ripe. The larva crawls out 
and up the tree and pupates 
in the bark. 

Among these pests, the 
most important to the dweller 
in a large city is the tussock 
moth, which destroys the 
leaves of the shade trees. The 
caterpillar may be recognized 
easily by its long hairs of yellow, brown, and black, and a tuft of 
red on its head. The cocoon is made of a combination of hairs 
and silk on the bark of a tree, or on a twig. The female has no 
wings and cannot crawl far. She lays her eggs, therefore, on 




Tussock moth: 1, adult male; 2, adult 
female, which has no wings; 3, larva; 
4, pupae; 5, female laying eggs. 



248 INSECTS — GENERAL CONSIDERATIONS 



the outside of the cocoon and dies a few hours later. The 
eggs remain over winter. By collecting and burning the egg 
masses in the fall, we may save many shade trees the following 
year. 

Other enemies of the shade trees are the fall webworm, the 
forest caterpillar, and the tent caterpillar; the last spins a tent 
which serves as a shelter in wet weather. 

The larv2e of some moths damage the trees by boring into the 
wood of the tree on which they live. Such are the peach, apple, 

and other fruit-tree borers 
common in our orchards. 
Some species of beetles pro- 
duce boring larvae which eat 
their way into trees and then 
feed upon the sap of the tree. 
Many trees in our Adiron- 
dack Forest Reserve annu- 
ally succumb to these pests 
because the beetle girdles 
the tree, cutting through 
the tubes in the cambium 
region. Most fallen logs 
will repay a search for the larvae which bore between the bark 
and wood. 

Among the insects most destructive to trees are the scale insects 
and the plant lice, or aphids. The San Jose scale, a native of 
China, was introduced into the fruit groves of California about 
1870 and has spread all over the country. It lives upon numer- 
ous plants, and is one of the worst pests this country has seen. 
It is interesting to know that a ladybird beetle, which has also 
been imported, is the most effective agent in keeping this pest 
in check. 

Insects of the House or Storehouse. — The weevils are the 
greatest pests, frequently ruining tons of stored corn, wheat, and 
other cereals. Roaches feed on almost any kind of breadstuffs as 
well as on clothing. The carpet beetle is a recognized foe of the 
housekeeper, the larvae feeding upon all sorts of woolen material. 
The larvae of the clothes moth do an inamense amount of damage 




San Jose scale, and a twig covered 
with the scales. 



BENEFICIAL INSECTS 249 

to stored clothing especially. Fleas, lice, and especially bedbugs 
are among man's personal foes.^ 

Beneficial Insects. — Fortunately for mankind, many insects 
are found which are of use because they either prey upon 
injurious insects or become parasites upon them, eventually 
destroying them. The ichneumon flies are examples already 
mentioned. They undoubtedly do much in keeping down the 
number of destructive caterpillars. 

Several beetles are of value to man. Most important of these 
is the natural enemy of the orange-tree scale, the lady bug, or 
ladybird beetle. In New York state it may often be found 
feeding upon the plant lice. The caloso'ma beetle preys upon 
the gypsy moth. The carrion beetles and many water beetles act 
as scavengers. The sexton beetles bury dead carcasses of animals. 
Ants in tropical countries are particularly useful as scavengers. 

Insects, besides pollinating flowers, often do a service by 
eating harmful weeds which are thus kept in check. We have 
noted that insects spin silk, thus forming clothing, that in many 
cases they are preyed upon, and support an enormous multitude 
of birds, fish, and other animals with food. 

How the Damage done by Insects is Controlled. — The com- 
bating of insects by the farmer is controlled and directed by two 
bodies of men, both of which have the same end in view. These 
are the Bureau of Entomology of the United States Department 
of Agriculture and the various state experiment stations. 

The Bureau of Entomology works in harmony with the other 
divisions of the Department of Agriculture, giving the time of its 
experts to the problems of controlling insects which, for good or 
ill, influence man's welfare in this country. Such problems as 
the destruction of the malarial mosquito and the control of the 
typhoid fly; the destruction of harmful insects by the intro- 
duction of their natural enemies, plant or animal; the perfecting 
of the honeybee (see Hodge, Nature Study and Life, page 240), 
and the introduction of new species of insects to pollinate flowers 
not native to this country (see the fig wasp, page 36) , are a few 
of those to which these men devote their time. 

1 Directions for the treatment of these pests may be found in pamphlets 
issued by the U.S. Department of Agriculture. 

HUNT. NEW ES. 17 



250 INSECTS — GENERAL CONSIDERATIONS 

All the states and territories have, since 1888, established 
state experiment stations, which work in cooperation with the 
government in the war upon injurious insects. These stations 
are often connected with colleges, so that young men who are 
interested in this kind of natural science may have opportunity 
to learn and to help. Bulletins are published by the various state 
stations and by the Department of Agriculture, most of which 
may be obtained free. The most interesting are the Farmers' 
Bulletins, issued by the Department of Agriculture, and the 
pamphlets issued by Cornell University in New York state. 

TABLE SHOWING A FEW INSECTS OF ECONOMIC IMPORTANCE 
AND MEANS FOR THEIR CONTROL OR EXTERMINATION 

1. Beneficial Insects 

Silk Moth. — Larva spins a cocoon from which silk is made. 

Honeybee. — Adult produces honey and pollinates flowers. 

Bumblebee. — Adult pollinates red clover and fruit trees. 

Ichneumon Fly. — Female lays eggs in the bodies of harmful larvae (as the 

grapevine caterpillar and the tree borers). The developing parasites 

feed on the hosts and kiU them. 
Dragon Fly. — Adult feeds on mosquitoes. 
Ladybird Beetle. — Adult feeds on scale insects and aphids. 
Gall Insect. — The developing larvse cause galls from which ink is made. 

2. Household Pests 

House Fly. — Adult carries typhoid, tuberculosis, and summer complaint 
and other intestinal diseases. To exterminate, it is necessary to prevent 
breeding and kill overwintering flies. 

Mosquito. — Adult carries malaria and yellow fever. May be exterminated 
by destroying the breeding places. See page 243. 

Body louse. — Adxxlt carries typhus. Insects may be killed by sterilizing 
infected clothing and by bathing patients in an antiseptic solution. 

Flea on Rats. — Adult carries bubonic plague. Kill the rats. 

Clothes Moth. — Larvae eat clothing: wool, fur, etc. They may be controlled 
by shaking or brushing the clothing, and exposing it to the sun. The use 
of camphor or naphthaline with clothing which is packed away deters 
the moth from laying its eggs there. 

Buffalo Carpet-Beetle. — Larva eats carpets. Spray benzine in the cracks in 
the floor and on the carpet. 

Cockroach. — Adults are scavengers and are numerous around sinks and 
where food is kept. They may be exterminated with poison bait. Clean- 
liness is necessary. 



CONTROL OF INSECTS 251 



3. Garden and Fruit Tree Pests 

Potato Beetle. — Larva eats leaves of the potato plant. Spray infected 

plants with arsenate of lead or Paris green. 
Cabbage Butterfly. — Larva eats leaves of cabbages and may be destroyed by 

a spray of arsenate of lead or Paris green. 
Hawk Moths. — Larva feeds on leaves of grape and tomato vines. Spray. 
Rose Beetles. — Adults feed on leaves and blossoms of the rose. Spray with 

a soap solution. 
Codling Moth. — Larva injures apples and pears. Spray with arsenate of 

lead at the time petals faU. 
San Jose Scale. — Adults suck juices from the leaves and young twigs of 

fruit trees. Killed by ladybird beetles and fumigation. 
Aphids. — Adult females suck juice from leaves and young twigs. Spray 

with nicotine sulphate. 
Boll-worm or Corn Worm. — Larva Uves in the ears of corn. 
European Corn Borer. — Feeds on stalks, roots, and ears of corn plant. Con- 
trolled by burning cornstalks in the faU. 

4. Forest and Shade Tree Pests 

Tussock Moth. — Larva eats leaves of shade and fruit trees. Destroy egg 

masses and spray in early spring. 
Gypsy Moth. — Damage and extermination the same as for tussock moth. 
Forest Tent Caterpillar. — Larva eats leaves of shade and fruit trees. Destroy 

nests and spray. 

Summary. — We find first that because of numerous adap- 
tations found in protective resemblance, mimicry, communal life, 
and symbiotic relationships that insects are the dominant forms 
on the earth to-day. 

Secondly, because they are so numerous and carry certain 
diseases insects are of much economic importance. Not only do 
they take toll of one tenth or more of the world's plant food 
supply but they are responsible for all yellow fever and malaria 
as well as most of our typhoid, dysentery, and bubonic plague. 

Problem Questions. — 1. Explain protective and aggressive 
resemblance. 

2. What is warning coloration? 

3. What is mimicry? 

4. Describe the communal life of the honeybee. 

5. What is symbiosis? Explain. 



252 INSECTS — GENERAL CONSIDERATIONS 

6. Explain how mosquitoes do harm. How may they be 
controlled ? 

7. Discuss the methods for prevention of yellow fever. 

8. Make a balance sheet giving harm and good caused by 
insects. 

Problem and Project References 

Cragin, Our Insect Friends and Foes. G. P. Putnams Son3. 

Crary, Textbook of Field Zoology: Insects and their Near Relatives and Birds. 

P. Blakiston's Sons and Company. 
Division of Entomology, Bulletins 1, 4, 5, 12, 16, 19, 23, 33, 34, 35, 36, 47, 48, 

61. U.S. Dept. of Agriculture. 
Doane, Insects and Disease. Henry Holt and Company. 
Folsom, Entomology; with Reference to its Biological and Economic Aspects. 

P. Blakiston's Sons and Company. 
Howard, Mosquitoes and Their Control. University of Minnesota, Agricultural 

Experiment Station. 
Hunter, Laboratory Problems in Civic Biology (Insect Bibliography). American 

Book Company. 
Hunter and Whitman. Civic Science. American Book Company, 
Lubbock, Bees, Ants and Wasps. D. Appleton and Company. 
Sharpe, Laboratory Manual. American Book Company. 



XXL THE MOLLUSKS 

Problem, A study of mollusks and their enemies with refer" 
ence to their economic importance. (Laboratory Manual. 
Prob. XXXIII; Laboratory Problems, Prob. 119.) 

To some high school pupils a clam or oyster on the " half 
shell" is a familiar object. The soft "body" of the animal 
Ijang between the two protecting "valves" of the shell gives the 
name to this group (Latin mollis — soft). Most mollusks have 
a shell composed mostly of hme, either bivalve (two-valved), 
as the oyster, clam, mussel, and scallop, or univalve (with one 
valve), as the snail. Usually the univalve shell is spiral in form. 
Among nature's most beautiful objects are the spiral shells of 
some marine forms. Other mollusks, for example the garden 
slug, have no shell whatever, and one highly speciaUzed form, 
the squid, has an internal shell. 

The limy shell, when present, is formed from the outer surface 
and edge of a delicate body covering called the mantle. The 
mantle may be found in the opened oyster or clam sticking 
close to the inside of the valve of the shell in which the body 
rests. Between the mantle and the body of the clam or oyster 
is a space, the mantle cavity, in which hang the platelike striated 
gills. By means of cilia on the inner surface of the mantle and 
on the gills a constant current of water is maintained through 
the mantle cavity, bearing oxygen to the gills and carbon 
dioxide away from them. This current of water passes, in most 
mollusks, into and out from the mantle cavity through the 
si'yhons; the muscular tubes forming the ''neck" of the ''soft 
clam" are examples of such organs. 

The food of clams or oysters consists of tiny organisms which 
are carried in the current of water to the mouth of the animal, 
this water current being maintained in part by the action of 
cilia on the palps or Hplike flaps surrounding the mouth. A 
single muscular foot enables the clam to move about slowly, 

253 



254 



THE :mollusks 




Shell of fresh-water elaru. the left half polished 
to show the prismatic layer from which buttons 
are made. 



The shallow water of bays where clams and oysters live, 
literalh' swarms with microscopic organisms which find the con- 
ditions for growth ideal. The tiny plants living there get food 
from the organic wastes brought down by the rivers. The 
carbon dioxide from the thousands of species of fish, mollusks, 

crustaceans, worms, and 
other forms of animal Hfe 
gives them another 
source of raw food 
material. The sunlight 
penetrating through the 
shallow waters supplies 
the energy for making 
the food. Thus condi- 
tions are ideal for rapid 
multiplication; hence 
the water becomes alive with the lower forms of plant life, 
among which are always found bacteria, both harmless and 
harmful. In feeding upon these plants, mollusks take in many 
bacteria; man feeds on the mollusks, and, if he eats them raw, 
may eat living bacteria as well. If the germs of typhoid fever 
are present, disease may result. 
As a matter of fact, epidemics 
of typhoid fever have been 
traced to such sources. 

Some Common Mollusks. — 
The fresh-water clam, a com- 
mon resident in the shallow 
water of inland ponds and 
rivers, has been sought in the 
making of pearl buttons. 
This industry is so important 

that it has depleted the number of adult clams in our Middle 
West : and the states affected and the United States government 
have undertaken the study of the life habits of these animals 
with a \new to restocking the rivei's. The development of the 
fresh-water clam or mussel is complicated. The egg develops 
into a free-s^'imming larval form which fastens to the gill of a 




Ciam sh 



;1 after the removal of disks 
for making buttons. 



CLAMS AND OYSTERS 



255 



fish and there lives as a parasite until almost mature. Then it 
drops off into the sand of the river or lake where it spends the 
rest of its Ufe. 

The Oyster. — Oysters are never found in muddy water, for 
they would be quickly smothered by the sediment. They cling 
to stones or shells or other objects which project a little above 
the bottom. Here food is abundant and oxygen is obtained from 
the air in the water 
surrounding them. 
Hence oyster raisers 
throw oyster shells 
into the water to 
make places of at- 
tachment for the 
young oysters. 

In some parts of 
Europe and of this 
country where 
oysters are raised 
artificially, stakes or 
brush are sunk in 
shallow water so 
that the young 
oysters, after the 
f r ee-s wimming 
stage, may find some 
object to which they 

can fasten and escape the danger of smothering on the bottom. 
After the oysters are a year or two old, they are taken up and 
planted in deeper water as seed oysters. At the age of three 
and four years they are ready for the market. 

The oyster industry is very profitable, amounting to over 
$15,000,000 a year during the last decade. Hundreds of boats 
and thousands of men are engaged in dredging for oysters. 
Three of the most important of our oyster grounds are Long 
Island Sound, Narragansett Bay, and Chesapeake Bay. 

Sometimes oysters are artificially ''fattened" by placing them 
near the mouths of fresh-water streams. These streams ofte^ 




Round clam (Venus merceneria) : AAM, anterior 
adductor muscle; ARM, anterior retractor muscle; 
PAM, posterior adductor muscle; PRM, posterior 
retractor muscle; F, foot; C, cloacal chamber; 
IS, in current siphon; FS., excurrent siphon; EO, 
heart; G, gills; M, mantle; DGL, digestive glands; 
S, stomach; I, intestine; P, palp; R, posterior end 
of digestive tract. 



25t> THE MOLLUSKS 

contain sewage. As this is a menace to health, it is evident that 
state and city supervision ought to be exercised not only to 
forbid the sale of shellfish which come from contaminated 
locaHties, but also to prevent the planting of oysters or other 
mollusks in the neighborhood of the openings of sewers or 
polluted rivers. ' 

Clams. — Other bivalve mollusks used for food are clams and 
scallops. Two species of the former are known to New Yorkers, 
one as the "round," the other as the ''long" or ''soft-shelled" 
clam. The round clam was called "quahog" by the Indians, 
who used the blue area of its shell as wampum, or money. Both 
species are prized for food. The clam industries of the eastern 
coast aggregate over $1,000,000 a year. 

Scallop. — The scallop, another moUuscan dehcacy, forms an impor- 
tant fishery. Only the single adductor muscle is eaten, whereas in the 
clam and oyster aU the soft parts of the body are used as food. 

Pearls and Pearl Formation. — Pearls are prized the world over. It 
is a well-known fact that even in this country pearls of some value are 
found occasionally within the shells of such common bivalves as the fresh- 
water mussle and the oyster. Most of the finest pearls, however, come from 
the waters around Ceylon. If a pearl is cut open and examined carefully, 
it is found to be a deposit of the mother-of-pearl layer of the shell around 
some central structure. It has been believed that any foreign substance, 
as a grain of sand, might irritate the mantle at a given point, thus stimu- 
lating it to secrete around the substance. It now seems likely that most 
perfect pearls are due to the growth within the mantle of the clam or 

oyster of certain parasites, which 

^^^^^f/esoffTe/jrec/CS ^^^ stages in the development of 

^' •^ the fluke worm. The irritation 

thus set up in the tissue causes 

mother-of-pearl to be deposited 

'Tentacle, around the source of irritation, 

mouth^^ olfactory nerve wi*^ ^^^ subsequent formation of 
endfngs a pearl. 

A common snail. Gastropods. — Snails, whelks, 

slugs, and the like are called ga&'- 
*/ropods (stomach-footed) because the foot occupies so much space that most 
of the organs of the body, including the stomach, are covered by it. Most 
gastropods are partly covered by a more or less spirally formed shell which 
has but one valve, in which the body is twisted spirally. In the garden 
slug, the mantle does not secrete an external shell, and the naked body 
is symmetrical. 




HABITAT 



257 



Gastropods of various species do considerable damage, some in the 
garden, where they feed upon young plants, and others in the sea, where 
they bore into the shells of other Uving moUusks in 
order to get out the soft part of the body which 
they use as food. 

Cephalopods. — Another class of moUusks are 
those known as cephalopods (s6f'a-l6-p5dz). The 
name means head-footed. As the Figure shows, the 
mouth is surrounded with a circle of tentacles. The 
sheU is internal or lacking. The so-called pen of the 
cuttlefish is aU that remains of the shell in that 
form. A cuttlefish is strangely modified for the life 
it leads. It moves rapidly through the water by 
squirting water from the siphon. It can seize its 
prey with the suckers on its long tentacles and tear 
it in pieces by means of its horny, parrothke beak. 
It is protected from its enemies and enabled to 
catch its prey because of its abiHty to change color 
quickly. In this way the animal simulates its 
surroundings. The cuttlefish has, near the siphon, 
an ink bag which contains the black sepia. A few 
drops of this ink squirted into the water may 
effectually hide the animal from its enemy. 

To this group of animals belong also the octopus, 
or devilfish, a cephalopod known to have tentacles 
over thirty feet in length; the paper nautilus; 
and the pearly nautilus, the latter made famous by our poet Holmes. 




The squid. One fourth 
natural size. 



Habitat of the MoUusks. — MoUusks are found in almost all 
parts of the earth and sea. They are more abundant in temper- 
ate localities than elsewhere, but live also in tropical and polar 
countries. They are found in all depths of water, but by far 
the greatest number of species live in shallow water near the 
shore. The cephalopods stay near the surface of the ocean, 
where they prey upon small fish. The food supply evidently 
determines to a large extent where they live. Some moUusks 
are scavengers; others feed on living plants. 

We have found in the forms of moUusks studied that almost 
all of them live in the water. There is one large group which 
forms a general exception to this, certain of the snails and slugs 
called puVmonates. But even these animals are found in damp 
localities, and during a drought they become inactive and remain 
within their shells. The European snail imported to this country 



258 



THE MOLLUSKS 



as a table delicacy exists for months by plugging up the aperture 
of its shell with a mass of sluny material which later hardens, 
thus protecting the soft body within. 

Economic Importance. — In general the moUusks are of 
much economic importance. The bivalves especially form an 
important source of our food supply. Many of the mollusks 
also make up an important part of the food supply of bottom- 
feeding fishes. On the other hand, some mollusks, as nat'ica, 

bore into the shells of 
other mollusks and eat 
the animals inside. Some 
boring mollusks, for ex- 
ample the shipworm, do 
much damage to wharves, 
-VAhere they make their 
homes in the piles. Still 
otliers bore holes in soft 
rock and live there. 

The shells of mollusks 
are used to a large extent 
in manufactures and in 
the arts, and they are 
still used as money in 
some parts of the world. 
Sepia comes from the 
cuttlefish. 




Ventral or under surface of the starfish. 
The dark circle in the middle is the mouth, 
from which radiate the five ambulacra! 
grooves, each filled with four rows of tube 
feet. Photograph half natural size, by 
Davison. 



The Starfish. — By far the 

mo'st important enemy of the 
oyster and other salt-water 
mollusks is the starfish. The 
common starfish, as the name indicates, is shaped like a five-pointed star. 
A skeleton of lime which is made up of thousands of tiny plates gives 
shape to the body and arms. Slow movement is effected by means of 
tiny suckers, called tube feet. Breathing takes place through the skin. 
The mouth is on the under surface of the animal, and, when feeding, 
the stomach is protruded and wrapped around its prey. The body of the 
starfish, as well as that of the sea urchin and others of this group, is spiny; 
hence the name Echinoderm (^-ki'n5-d0irm), which means spiny-skinned, is 
given to the group. 
Food of the Starfish. — Starfish are enormously destructive o f young 



THE STARFISH 259 

clams and oysters, as the following evidence, collected by Professor A. D. 
Mead of Brown University, shows. A single starfish was confined in an 
aquarium with fifty-six young clams. The largest clam was about the 
length of one arm of the starfish, the smallest about ten millimeters in 
length. In six days every clam in the aquarium was devoured. 

In order to capture and kill mollusks, the starfish wrap themselves around 
the valves of the shell and actually pull them apart by means of their tube 
feet, some of which are attached to one valve and some to the other of their 
victim. Once the soft part of the mollusk is exposed, the stomach envelops 
it and covers it with the secretions of digestive glands, and it is rapidly 
digested and changed to a fluid. 

Hundreds of thousands of dollars' damage is done annually to the 
oysters in Connecticut alone by the ravages of starfish. During the sum- 
mer months the oyster boats are to be found at work raking the beds for 
starfish, which are collected and thrown ashore by the thousands 

Classification op Mollusks (Mollusca) 

Class I. Pelecyp'oda {Lamellibranchia'ta) . Soft-bodied unsegmented ani- 
mals showing bilateral symmetry. Bivalve shell, platelike gills. Ex- 
amples: clam, scallop, oyster, and fresh-water mussel. 

Class II. Gastrop'oda. Soft bodies asymmetrical; univalve shell or shell 
absent. Some forms breathe by gills, others by lunglike sacs. Ex- 
amples: pond snail, land snail, and slug. 

Class III. Cephalop'oda. Bilaterally symmetrical mollusks with mouth 
surrounded by tentacles. Shell may be external (nautilus), internal 
(squid), or altogether lacking (octopus). Examples: squid, octopus. 

Summary. — ^ Mollusks are characterized by a soft body, a man- 
tle which secretes the shell when present, and a muscular foot. 
Some are of economic importance as food, as the clam, scallop, 
and oyster. 

Problem Questions. - 1. How do mollusks move? 

2. How do mollusks breathe? 

3. On what kind of food do mollusks feed? 

4. How are pearls formed? 

5. How do starfish eat? Explain fully. 

Problem and Project RBFERBNcrBS 

Brooks, The Oyster. Johns Hopkins Press. 

Bulletin, U.S. Fish Commission, 1899. 

Kellogg, The Shellfish Industries. Henry Holt and Company. 

Parker, Lessons in Elementary Biology. The Macmillan Compjacy. 

Sharpe, Tjoboratory Manual. American Book Company. 



XXII. THE VERTEBRATE ANIMALS 

Increasing Complexity of Structure and of Habits in Plants 
and Animals. — In our study of biology so far we have at- 
tempted to get some notion of the various factors which act upon 
and interact with living things. We have learned something about 
the various physiological processes of plants and animals, and 
have found them to be in many respects identical. We have 
examined a number of forms of plants and have found all 
grades of complexity, from the one-celled plant, bacterium or 
pleurococcus, to the complicated flowering plants of considerable 
size and with many organs. So in animal life the forms we 
have studied, from the Protozoa upward, there is constant 
change, and the change is toward greater complexity of struc- 
ture and of function. A worm is simpler in structure than an 
insect, and shows by its sluggish actions that it is not so high 
in the scale of life as its more lively neighbor. 



/n/erfebrate 



Vertebrate 



t/e&rt---- 

Stfeteton- 

tnfest/neA' 



Jystemi 





SAeteto/i 
-Afese/jter/' 
-tC/ctneys 

-tntest/ne 

tlten^ous-.-^St^..^ m. ^ \^ (^-—:^—/feart 

System 

Cross section through an invertebrate animal and a vertebrate animal. 

We are already awake to the fact that we are better equipped 
in the battle for life than our more lowly neighbors, for we 
are thinking creatures, and can change our surroundings at 
will, while the lower forms of animals are largely controlled 
by stimuli which come from without; temperature, moisture, 

260 



FISHES — ADAPTATIONS 



261 



light, the presence or absence of food, — all these result in 
movement and other reactions. 

Our next study will be of a group of animals called ver'te- 
brates, because they have a bony vertebral column, made up of 
pieces of bone joined one to another, forming a flexible yet 
strong support for the muscles and protecting the delicate cen- 
tral nervous system. This kind of an endoskeleton, or inside 
skeleton, is possessed by fishes, frogs, turtles, snakes, birds, and 
mammals, such as the dog, the cat, and man. We begin with the 
study of some types of various kinds of vertebrates, with a view 
to the better understanding of man. 

Fishes 

Problem, To determine how a Ush is fitted for the life it leads, 
(Laboratory Manual, Prob, XXXIV; Laboratory Problems, 
Probs. 133 to 139.) 

The Body. — One of our common fresh-water fishes is the 
perch. The body of the perch, hke that of many other fishes, 



ftnsL cLorsal yliv^ 



lateral line 
nostril 



CocucLol Jir 




operculum . „ .- 
' -pectoral nvL 




^pelvic fin. 



Side view of a fish (a perch). There are two pectoral and 
two pelvic fins, one on each side. 

runs insensibly into the head, the neck being absent. The long, 
narrow body, pointed at the anterior end, with its smooth sur- 
face, makes the fish admirably adapted for swimming. Certain 
cells in the skin which secrete mucus or slime, and the position 
of the scales, overlapping in a backward direction, are other 
adaptations which aid the fish in passing through the water. 



262 THE VERTEBRATE ANIMALS 

The color of many fishes, oHve above and gray or bright silver 
below, is protective. Can you see how? 

The Appendages and their Uses. — The appendages of the 
fish consist of paired and unpaired fins. The paired fins are 
four in number, and are believed to correspond in position and 
structure with the paired limbs of a man. In the Figure 
(p. 261) locate the paired pectoral and pelvic fins. Compare a 
living fish with the Figure, and find the dorsal, anal, and caudal 
fins. How many unpaired fins are there? The study of a fin 
shows that it is composed of a thin membrane which is held in 
shape and stiffened by long slender rods of bone or cartilage 
called fin rays. The fin is light and strong, and, as powerful 
muscles are attached to it, can push against the water with 
sufficient force to move the body forward. Note that the dor- 
sal fin has spinelike rays, while the fin rays of the caudal fins 
are flexible. Do you find any fins in which both kinds of rays 
occur? 

The flattened, muscular body of the fish, tapering toward the 
caudal fin, is moved from side to side with an undulating mo- 
tion which results in the forward movement of the fish. This 
movement is almost identical with that of an oar in sculling a 
boat. Turning movements are brought about by use of the 
lateral fins in much the same way as a boat is turned. We 
notice that the dorsal and anal fins are evidently useful as 
balancing and steering organs. 

The Senses. — The position of the eyes at the sides of the 
head is an evident advantage to the fish. Why? The eye is 
globular in shape. As such an eye has been found to be very 
near-sighted, it is Hkely that a fish is unable to perceive objects 
at any great distance from it. The eyes are unprotected by 
eyeHds, but their tough outer covering and their position at the 
sides of the head afford some protection. 

Feeding experiments show that a fish becomes aware of the 
presence of food by smelling it as v/ell as by seeing it. The 
nostrils of a fish are organs for smelUng. They are little pits, 
which differ from our nostrils in that they are not connected 
with the mouth cavity. In the catfish, the harhels, or horns, 
receive sensations of smell and taste. The sense of smell in a 



FISHES 263 

fish is not quite the same as ours, for it perceives only substances 
that are dissolved in the water in which it lives. The senses of 
taste and touch appear to be less developed than the other 
senses. 

Along each side of most fishes is a line of tiny pits, provided 
with sense organs and connected with the central nervous sys- 
tem. This area, called the lateral line, is beheved to be sensitive 
to mechanical stimuli of certain sorts. The ''ear" of the fish 
is under the skin and serves partly as a balancing organ. 

The tongue in most fishes is wanting or very slightly de- 
veloped. 

Breathing. — A fish, when swimming quietly and when at rest, 
seems to be biting even if no food is present. It will be found 
that a current of water enters when the mouth is opened and 
is pushed back by the closing of the mouth and out through 
slits located on each side back of the head. Investigation shows 
us that under the broad, flat plate, or oper'culum, covering these 
slits on each side, lie several long, feathery, red structures, the 
gills. By the movements of the mouth a current of fresh water 
is made to pass over the gills. 

Gills. — In most fishes we find five pairs of gills. The founda- 
tion of the gill, or the gill arch, is composed of several pieces of 
bone which are hinged in such a way as to give great flexibility. 
Covering the bony framework, and extending from it, are numer- 
ous dehcate filaments of flesh, covered with a very delicate 
membrane or skin. In each of these filaments are two blood 
vessels; in one blood flows downward and in the other, upward. 
While in the gill filament the blood is separated by a thin mem- 
brane from the oxygen dissolved in the water bathing the gills. 
An exchange of gases through the walls of the gill filaments 
results in a loss of carbon dioxide and a gain of oxygen by the 
blood. 

Gill Rakers. — If we open wide the mouth of any large fish 
and look inward, we find that the mouth cavity leads to a 
funnel-like opening, the gullet. On each side of the gullet we 
can see the gill arches holding the red filament. These delicate 
structures are guarded on the inner side by a series of sharp- 
pointed structures, the gill rakers. In some fishes in which the 



264 THE VERTEBRATE ANIMALS 

teeth are not well developed, there is a greater development of 
the gill rakers, in which case they are used to strain out food 
or small organisms from the water which passes over the gills. 
(See Figure, p. 266.) 

Digestive System. — The gullet leads directly into a baglike stomach. 
There are no salivary glands in the fishes. There is, however, a large 
liver, which appears to be used as a digestive gland. The liver contains a 
good deal of oil and therefore is • in some fishes, as the cod, of considerable 
economic importance. Many fishes have outgrowths like a series of pockets 
from the intestine. These structures, called the pylor'ic cceca (se'ka), are 
believed to secrete a digestive fluid. The intestine ends at the vent, or 



Smblddder 




Bdrbels 

&//i/3*^~* Small intestine 

Anatomy of a fish (a carp). 

anus, which is usually located on the ventral side of the fish, immediately in 
front of the anal fin. 

Swim Bladder. — An organ of unusual significance, called the swim 
bladder, occupies the region just dorsal to the food tube. In young fishes 
of many species this is connected by a tube with the anterior end of the 
digestive tract. In some forms this tube persists throughout life, but in 
other fishes it becomes closed, and makes a thin, fibrous cord. The size 
of the swim bladder can be changed through the contraction or expansion 
of its walls. The fish uses it to make changes in the space it occupies, 
so that the water displaced will equal its own weight. Thus the weight 
of the fish is supported, no matter at what depth it wishes to remain. 

Circulation of the Blood. — In the vertebrate animals the blood circulates 
around the body, through a more or less closed system of tubes. In fishes 
the heart is a muscular organ, with two connecting chambers: a thin-walled 
au'ricle, or receiving chamber, and a thick-walled muscular ventricle from 
which the blood is forced out. The blood is pumped from the heart to the 
gills, wjiere it loses carbon dioxide and receives oxygen; it then passes on to 



FISHES 265 

other parts of the body, until it reaches very tiny tubes called cap'illaries. 
From the capillaries the blood returns, in veins of gradually increasing 
diameter, to the heart again. During its course around the body some of 
the blood passes through the kidneys and is there relieved of its nitrogenous 
waste. (See Chapter XXVII.) 

Circulation of blood in the fish is rather slow. The temperature of the 
blood is nearly that of the water in which the fish lives. 

Nervous System. — As in aU other vertebrate animals, the central 
nervous system of the fish consists of the brain and spinal cord, which are 
covered by cartilage or bone for protection. The brain has nerves leading 
to the organs of sight, taste, and smell, to the ear, and to such parts of 
the body as possess the sense of touch. Nerve cells located near the outside 
of the body send messages to the brain, where they are received as sensa- 
tions. Cells of the central nervous system, in turn, send out messages which 
result in the movement of muscles. 

Skeleton. — In the vertebrates, of which the bony fish is an example, 
the skeleton is under the skin, and is hence called an endoskeleton. It 
consists of a skuU, the vertebral column, the ribs, and other spiny bones 
to which the unpaired fins are attached. The paired fins are attached to 
the spinal column by two collections of bones, known respectively as the 
pectoral and pelvic girdles. The bones serve in the fish for the attachment 
of powerful muscles, by means of which locomotion is accomplished. In 
most fishes the exoskeleton, too, is well developed, modifications appearing 
from scales to complete armor. 

Problem. To determine some of the relations of fishes to their 
food supply. {Laboratory Manual, Prob. XXXV; Laboratory 
Problems, Prob. 139.) 

Food of Fishes. — We have already seen that in a large 
balanced aquarium the plants furnish food for the tiny 
animals and a few of the larger ones, — for example, snails. 
The smaller animals are eaten by larger ones until the largest 
of all is fed. The nitrogen balance is maintained through 
the wastes of the animals and their death and decay. 

The ocean is a great balanced aquarium in which the upper 
layer of water is crowded with all kinds of little organisms, both 
plant and animal. Although microscopic in size or barely 
visible to the eye, like the tiny crustaceans, they serve as food 
for big fishes. The menhaden ^ (bony, bunker, mossbunker of 

^ It has been discovered by Professor Mead of Brown University that the in- 
crease in starfish along certain parts of the New England coast was in part due 
to overfishing of menhaden, which at certain times in the year feed almost en- 
tirely on the young starfish. 

HUNT. NEW. EB. 18 



266 



THE VERTEBRATE ANIMALS 






Oillarch Cillrakers 
QUI filament 




CHI arch 
dill filament 



Comparative size of mouth in bluefish (large 
mouth) and shad (small mouth and large gill 
rakers) . 



our coast), the shad, and others, depend upon these minute 
organisms for food. Such fishes have small mouths and very 
large gill rakers which strain the water as it passes over the 

-, gills and hold back the 

B'^^f'^f" ^^ -^ food particles. Other 

fishes are bottom feeders, 
as the blackfish and the 
sea bass, living almost 
entirely upon moUusks 
and crustaceans. Still 
others are hunters, feed- 
ing upon smaller species 
of fish or even upon 
their weaker brothers. 
Such are the bluefish, 
and the squeteague or weakfish. Such a fish must go after its 
prey and seize it with its mouth, as it has no grasping organs 
except its teeth. Consequently we find a large mouth in which 
the teeth are sharp, pointed, numerous, and adapted for holding 
living prey. The gill rakers are small or lacking. 

What is true of salt-water fish is equally true of those in- 
habiting our fresh-water streams and lakes. It is one of the 
greatest problems of our Bureau of Fisheries to discover this 
relation of various fishes to their food supplies so as to aid in 
the conservation and balance of life in our lakes, rivers, and 
seas. 

The Egg-laying Habits of the Bony Fishes. — The eggs of 
most bony fishes are laid in great numbers. The number varies 
from a few thousand in the trout to many hundreds of thou- 
sands in the shad and several millions in the cod. The time of 
spawning is usually spring or early summer. After the eggs 
are laid the male usually deposits milt, consisting of millions of 
sperm cells, in the water just over the eggs. The sperm cells 
move rapidly through the water, find the egg cells, and fertili- 
zation follows. Some fishes, as sticklebacks, sunfish, toadfish, 
etc., make nests, but usually the eggs are left to develop by 
themselves, sometimes attached to some submerged object, but 
more frequently free in the water, Some eggs which have a 



FISHES 



267 



tiny oil drop, are buoyed up to the surface, where the heat of 
the sun aids development. Both eggs and developing fish are 
exposed to many dangers, and are eaten, not only by birds, 
fish of other species, and other water inhabitants, but also by 
their own relatives and even parents. Consequently a very 
small percentage of eggs ever reach maturity. 

Life History of the Yellow Perch. — This common fish has 
been caught by almost every boy who reads these fines. It 
frequents inland ponds and streams in the northeastern part 




Life history of a fish: 1, 2, developing eggs; 3, 4, young with yolk sac; 
5. 6, 7, later stages after the yolk sac is absorbed. 

of the United States. Large numbers of them roam about 
in schools so that if one locates a school he may be fairly sure 
of a good catch. 

Perch lay their eggs in masses or strings, often several hundreds 
or even thousands being found in a single mass. The time of egg 
laying is in March or April. After fertilization the eggs segment, 
forming a mass of cells, which gradually assume the form of a 
tiny fish with a yolk sac, containing food, on its ventral surface. 
Eventually the yolk is absorbed by the young fish and a few 
weeks from the time of hatching we find it able to take care of 
itself. ^ 

Life History of the Chinook Salmon. — The Chinook salmon 
of the Pacific coast is the salmon used in the western canning 



268 



THE VERTEBRATE ANIMALS 




Salmon leaping a fall on the way to 
their spawning beds. 



industry. It is a fine, big fish, of about four or five years, when 
it reaches maturity, leaves the Pacific, and enters the Columbia 
or one of the other big rivers of the western slope to journey 
to the cool mountain streams, where it spawns. During this 

journey of from one thou- 
sand to two thousand miles, 
it does not eat, swims against 
a strong current, and leaps 
high falls. The salmon start 
in early spring. Large num- 
bers of them pass up the 
rivers together and reach the 
spawning beds in late sum- 
mer in a very exhausted 
condition. Here the fish re- 
main until the temperature 
of the water falls to about 
54° Fahrenheit. Shallow 
nests are made in the gravel by. the male. The eggs and 
milt are then deposited, and the old fish die, leaving the eggs 
to be hatched out thirty or forty days later by the heat of 
the sun's rays. The young salmon pass down stream to the 
ocean, where they live until mature, when they return to the 
rivers to lay their eggs. 

Migration of Fishes. — Some fishes change their habitat at 
different times during the year, moving in vast schools north- 
ward in summer and southward in the winter. In a general 
way such migrations follow the coast lines. Examples of the 
migratory fish are the cod, menhaden, herring, and bluefish. 
The migrations are due to temperature changes, to the seeking 
after food, and to the spawning instinct. T'he salmon, shad, 
sturgeon, and smelt pass up rivers from the ocean to lay their 
eggs. Some fish migrate to shallower water in the summer and 
to deeper water in the winter; here the reason for the migration 
is doubtless the change in temperature. The instinct of salmon 
and other species to go into shallow rivers to deposit their eggs 
has been made use of by man. At the time of the spawning 
migration the salmon are taken in vast numbers, 



FISHES 



269 



Economic Importance. — Fish are of great importance as food. 
The herring fisheries have always been a source of wealth to 
the inhabitants of northern Europe. The banks and shallows 
of the coast of Newfoundland abound in cod. The cod fisheries 
of the United States net over $20,000,000 a year, the salmon 
fisheries over $16,000,000, the shad at least $1,500,000, the smelt 
fishery nearly $150,000. The total annual value of the fisheries 
of the United States is over $50,000,000. 




The bones of fish are ground and made into fertilizers. Soap 
is made from the oil of fish. Cod liver oil is used as a medi- 
cine. Glue is made from the skin, fins, etc. 

Problem. To learn something of the artificial propagation of 
fishes. {Laboratory Manual, Proh. XXXVI.) 

The Work of National and State Governments in protecting 
and propagating Food Fishes. — But the profits from the 
fisheries are steadily decreasing because of the yearly destruc- 
tion of untold millions of eggs which might develop into adult 
fish. 

Fortunately, the United States government through the 
Bureau of Fisheries, and various states by wise protective laws 
and by artificial propagation of fishes, are beginning to turn 
the tide. Certain days of the week the salmon are allowed to 
pass up the Columbia unmolested. Closed breeding seasons 



S70 



THE VERTEBRATE ANIMALS 



protect our trout, bass, and other game fish. The catching of cer- 
tain fish under a stated size is prohibited also. Many fish hatch- 
eries, both national and state, are engaged in artificially fertilizing 
millions of eggs of various species and protecting the young fry 
until they can be placed in ponds or streams at a size when 
they can take care of themselves. For artificial fertihzation the 
ripe eggs of a female are squeezed out into a pan of water; in 




Work of a fish hatchery: fertilization of eggs. Two men with dipnets are lifting 
male and female whitefish from crates into the tub at the right. The spawntaker 
presses out the eggs and the milt into a pan, which is passed on to the man at the 
left. After washing and hardening, the eggs are removed to the hatchery. 

a similar manner the milt or sperm cells are obtained, and 
poured over the eggs. The fertilized eggs are carefully pro- 
tected, and, after hatching, the young fry are kept in ideal con- 
ditions until later they are shipped, sometimes thousands of 
miles, to their new home. 

It is feared in many cases that assistance comes too late, for at 
the present rate of destruction some of our most desirable 
food fishes will soon be extinct. The sturgeon, the eggs of 
which are used in the manufacture of the delicacy known as 
caviare, is an example of a fish that is almost extinct in this 



FISHES 



271 



part of the world. The shad is found in fewer numbers each 
year, and in fewer rivers as well. The salmon will undoubtedly 
soon meet the fate of other fishes which are taken at the 
spawning season, unless conservation of a radical sort takes 
place. 

Classification of Fishes 

Subclass I. Elasmobran' chii. Fishes having a skeleton formed of carti- 
lage which has not become hardened with lime; gills communicating 
with the surface of the body by separate openings instead of having 
an operculum. Examples: sharks, rays, skates. 




Sand shark, an elasmobranch. Note the slits leading from 
the gills. From photograph loaned by the American Museum 
of Natural History, 

Subclass II. Ganoi'dei. Fishes having bodies protected by a series of 
platelike scales of considerable strength. Example: gar pike. 




Sturgeon, a ganoid. 



Subclass III. Teleos'tei. Fishes having a bony skeleton; gills pro- 
tected by an operculum. These tel'eosts comprise 95 per cent of all 
living fishes. 

Subclass IV. Dip'noi. A very small group of fishes that use the swim 
bladder as a lung. They are thus in some respects like amphibians. 
They live in tropical Africa, South America, and Australia, where 
rivers and lakes go dry for part of the year. 

Summary. — Fish are animals adapted to an aquatic life by 
having a smooth, more or less cigar-shaped body, with modi- 



272 THE VEK.TEBRATE ANIMALS 

fied flattened appendages called fins and a powerful caudal fin 
which serves with the muscles of the body as an organ of lo- 
comotion. Gills absorb oxygen which is dissolved in the water 
and give off carbon dioxide. Fishes usually lay large numbers 
of eggs, and many of the young die before reaching maturity. 
The egg-laying habits often take fish, as the salmon, thousands 
of miles up rivers to lay their eggs. Fishes are of great 
economic importance as food and need protection from govern, 
ment and individuals alike. 

Problem Questions.' — 1. What adaptations enable a fish to 
swim? to escape its enemies? to catch its prey? 

2. Discuss the egg-lajdng habits of some specific fishes. How 
do you account for the differences in habits? 

3. Classify the fishes. 

Problem and Project References 

Davison, Practical Zoology, pages 185-199. American Book Companj'. 
Herrick, Textbook in General Zoology, Chap. XIX. American Book Company, 
Hunter, Laboratory Problems in Civic Biology. American Book Company. 
Jordan, Fishes. Henry Holt and Company. 
Jordan and Evermann, American Food and Game Fishes. Doubleday, Page, and 

Company. 
Jordan, Kellogg, and Heath, Animal Studies, XIV. D. Appleton and Company. 
Sharpe, A Laboratory Manual. American Book Company. 

Amphibia. The Frog 

Problem. To discover some adaptations in a living frog. 
(Laboratory Manual, Prob. XXXVII; Laboratory Problems^ 
Probs. 140 to 145.) 

Adaptations for Life. — The most common frog in the eastern 
part of the United States is the leopard frog. It is recognized 
by its greenish brown body with dark spots, each spot being 
outlined in a lighter colored background. In spite of the ap- 
parent lack of harmony with its surroundings, its color, on 
the contrary, appears to give almost perfect protection. In 
some species of frogs the color of the skin changes with the 
surroundings of the frog, another means of protection. 

Adaptations for life in the water are numerous. The ovoid 



THE FROG 



273 



- , - -^»!^r. - ."^^w-T^^i^wrai^M^* *3"'nwiBr? j~,m 




^^^'iL^ 


'"'OiiTiMili^jfli „''* 












\..l 


^^^1 


t ^ 




4;' 


^ 


X 


-^'■■j^m 


■*; 




" ■"**^* 9 


' .4^1 



body, the head merging into the trunk, the slimy covering 
(for the frog is provided, Hke the fish, with mucus cells in the 
skin), and the powerful legs with webbed feet, are all evidences 
of the life which the frog leads. 

Locomotion. — You will notice that the appendages have the 
same general position on the body and same number of parts 
as do your own (upper 
arm, forearm, and hand; 
thigh, shank, and foot, the 
latter much longer rela- 
tively than your own). 
Note that while the hand 
has four fingers, the foot 
has five long toes, con- 
nected by a web to push 
against the water when 
swimming. As the frog 
lives on both land and 
water its powerful, long 
legs are adapted for jump- 
ing as well as for swimming. When at rest, these legs are doubled 
up close to the body ready to give a quick spring forward. As 
they are very long and attached to powerful muscles, the frog 
moves rapidly. The short arms are used to balance the body 
when at rest. 

Sense Organs. — The frog is well provided with sense organs. 
The eyes are large, globular, and placed at the sides of the head. 
When the frog goes under water a delicate fold, called the 
nictitating membrane (or third eyelid), is drawn over each eye. 
Frogs probably see moving objects best at a few feet from 
them. Their vision is much keener than that of the fish. 
The external ear (tym'panum) is located just behind the eye on 
the side of the head. Frogs hear sounds and distinguish vari- 
ous calls of their own kind, as is proved by the fact that they 
recognize the warning notes of their mates when any one is 
approaching. The inner ear has to do with balancing the body 
as it does in fishes and other vertebrates. Touch is a well- 
developed sense. Frogs respond to changes in temperature 



The leopard frog. 



274 



THE VERTEBRATE ANIMALS 



under water, and go into a dormant state for the winter when 
the temiperature of the air becomes colder than that of the water. 

Taste and smell are probably not strong sensations in a frog 
or toad. 

Food Getting. — The frog's mouth is large and the sticky 
tongue is long and flexible. It is attached to the front of the 
floor of the mouth and is thrown out with great rapidity to secure 






How a frog catches a fly. 

living prey. Experience has taught these animals that mov- 
ing things, insects, worms, and the like, make good food. These 
they swallow whole, the tiny teeth being used to hold the 
food. 

Breathing. — The frog takes air into its mouth by lowering 
the floor of the mouth and pulling in air through the two nos- 
tril holes. Then the little flaps over the holes are closed, the 
floor of the mouth is raised, and the frog swallows this air, 
thus forcing it down into the baglike lungs. When the nos- 
tril flaps are lifted the air is forced out by the pressure of the 
body wall and the elasticity of the lungs. The lungs contain air 
spaces, the walls of which are filled with blood vessels. Some of 
the oxygen from the air passes through the walls into the 
blood, while some of the carbon dioxide of the blood in turn is 
passed into the air in the lung sacs. The skin also is provided 
with many tiny blood vessels which absorb oxygen and give off 
carbon dioxide. In winter, while the frogs are dormant at the 
bottom of the ponds, the skin is the only organ of respiration. 

The Food Tube and its Glands. — The mouth leads hke a 
funnel into a short tube, the gullet. On the lower floor of the 
mouth can be seen the slitlike glottis or opening into the trachea. 
The gullet widens almost at once into a long stomach, which 
in turn leads into a narrow, much coiled intestine. This widens 



THE FROG 



275 



abruptly into the cloa'ca (Latin, sewer) into which open the kid- 
neys, urinary bladder, and reproductive organs {ovaries or sper- 
maries). Several glands, the function of which is to produce 
digestive fluids, open into the food tube. These digestive fluids 
by means of the ferments 
or enzymes contained in 
them, change insoluble 
food materials into a 
soluble form so that they 
may be absorbed through 
the walls of the food tube 
and become part of the 
blood. The glands (hav- 
ing the same names and 
uses as those in man) are 
the salivary glands, which 
pour their juices into the 
mouth, the gastric glands 
in the walls of the stomach, 
and the liver and pancreas, 
which open into the in- 
testine. (See Digestion, 
chapter XXV.) 

Circulation. — The frog has 
thick-walled muscalar ^^entricle 



deart—i-^' 



SmdII Intestine - 

Spleen-- ^"^ 
Large Intestine 




Mngs 
stiver 
Z-Oall Bladder 

^.Stomach 
L_ Pancreas 

fi^JJrindr/ Bladder 



Internal organs of a froR. 



a well-developed heart, composed of a 
and two thin-walled auricles. The heart 
pumps the blood through a system of closed tubes to all parts of the body. 
Blood enters the right auricle from all parts of the body; it then con- 
tains considerable carbon dioxide; the blood entering the left auricle comes 
from the lungs, hence it contains a considerable amount of oxygen. Blood 
leaves the heart through the ventricle, which thus pumps blood contain- 
ing much and little oxygen. Before the blood from the tissues and from 
the lungs has time to mix, however, it leaves the ventricle and, by a delicate 
adjustment in the vessels leaving the heart, most of the blood containing 
much oxygen is passed to all the various organs of the body, while the blood 
deficient in oxygen, but containing a large amount of carbon dioxide, is 
pumped to the lungs. 

In the cells of the body wherever work is done the process of burning 
or oxidation must take place, for by such means only is the energy nec- 
essary to do the work released. Food in the blood is taken to the muscle 
cells or other cells of the body and there oxidized. The products of the 
burning, chiefly carbon dioxide, and any other organic wastes given off from 



276 THE VERTEBRATE ANIMALS 

the tissues must be eliminated from the body. As we loiow, the carbon 
dioxide passes off through the kmgs and to some extent through the skin 
of the frog, while the nitrogenous wastes, poisons which must be taken 
from the blood, are eliminated from it in the kidneys. 

Problem, To learn about the development of a frog, {Labora- 
tory Manual, ^ Prob. XXXVI; Laboratory Problems, Probs. 
146 to 148.) 

(a) Conditions favorable for development. 

(6) Metamorphosis. 

(c) Development of a toad (optional). 

Field and Home Work. — During the first warm days in March or 
April, look for gelatinous masses of frogs' eggs attached to sticks or water 
weeds in shallow ponds. Collect some and keep in a shallow dish in a 
window at home until they hatch. Make experiments to learn whether 
temperature affects the development of the eggs in any way. Place eggs 
in dishes of water in a warm room, in a cold room, and in the ice 
box. Make observations for several weeks as to the rate of development 
of each lot of eggs. Also try placing a large number of eggs in one dish, 
thus cutting down the supply of available oxygen, and in another dish 
near by, under the same conditions of light and heat, place a few eggs 
with plenty of water. Do both batches of eggs develop with the same 
rapidity? In all these experiments be sure to use eggs, from the same 
egg mass, so as to make sure that all are of the same age. 

Development. — The eggs of the leopard frog are laid in 
shallow water in the early spring. Masses of several hundred, 
which may be found attached to twigs or other supports under 
water, are deposited at a single laying. Immediately before leav- 
ing the body of the female they receive a coating of jellylike 
material, which swells up after the eggs are laid. Thus they are 
protected from the attacks of fishes or other animals which might 
use them as food. The upper side of the egg is dark, the light- 
colored side being weighted down with a supply of yolk (food). 
The fertilized egg soon segments (divides and subdivides into 
many cells), and in a few days, if the weather is warm, it has 
grown into an oblong body which shows the form of a tadpole. 
Shortly after, the tadpole wriggles out of the jellylike case and 
begins life outside the egg. At first it remains attached to 
some water weed by means of a suckerlike projection; later 
a mouth is formed at this point, and the tadpole begins to 



THE FROG 



277 



feed upon algae and other tiny water plants. At this time, 
about two weeks after the eggs were laid, gills are present on 
the outside of the body. Soon after, the external gills are re- 
placed by gills which grow out under a fold of the skin which 




Development of the frog: 1, 2, 3, eggs; 4, newly hatched tadpoles; 
5, tadpole with external gills; 6 to 11, later stages; 12, frog. 

forms an operculum somewhat as in the fish. Water reaches 
the gills through the mouth and passes out through a hole on 
the left side of the body. As the tadpole grows larger, legs 
appear. The hind legs grow out first. The tail is used as an 
organ for locomotion until the hind legs are ready. 



278 



THE VERTEBRATE ANIMALS 



Shortly after the legs appear, the gills are absorbed, and 
luDgs take their place. At this time the young animal may 
De seen coming to the surface of the water for air. Changes 
in the diet of the animal also occur; the long, coiled intestine 
is transformed into a much shorter one. The animal, now in- 
sectivorous in its diet, becomes provided with tiny teeth and a 
mobile tongue, instead of the horny jaws used in scraping 
off algae. After the tail has been completely absorbed and 
thf legs have become full grown, there is no further structural 
change, and the metamorphosis is complete. 

In the leopard frog the change from the egg to adult is com- 
pleted in one summer. In the green frog and bullfrog the 
metamorphosis is not completed until the beginning of the 

second summer. The 
large tadpoles of such 
forms bury themselves 
in the soft mud of the 
pond bottom during 
the winter. 

The Common 
Toad. — One of the 
nearest allies of the 
frog is the common 
toad. The eggs, like 
those of the frog, are 
deposited in fresh- 
water ponds. The egg- 
laying season of the 
toad is later than that of the frog. The eggs are laid in strings, 
and as many as eleven thousand eggs have been laid by a single 
toad. ^ 

Toad tadpoles may be distinguished from those of the frogs, as 
they are darker in color, and have a more slender tail and a 
relatively larger body. The metamorphosis occupies only about 
two months in the vicinity of New York, but varies gre^,tly 
with the temperature. During the warm weather the tail is 
absorbed with wonderful rapidity, and the change from a tad- 
pole with no legs to a small toad living on land^ is often 




The common toad. 



AMPHIBIANS 279 

accomplished in a few hours. This has given rise to the absurd 
story that it rains toads, because during the night thousands 
of young toads have changed their habitat from the water to 
the land. 

The toad is of great economic importance to man because 
of its diet. No less than eighty-three species of insects, mostly 
injurious, have been proved to enter into its dietary. A toad 
has been observed to snap up one hundred and twenty-eight 
flies in half an hour. At a low estimate it could easily destroy one 
hundred insects a day for several months, and do an immense 
service to the garden during the summer. It has been esti- 
mated by Kirkland that a single toad may, on account of the 
cutworms that it kills, be worth $19.88 a season, if the damage 
done by each cutworm be estimated at only one cent. Toads 
also feed upon slugs and other garden pests. 

Other Amphibians. — The tree frogs (called tree toads) are familiar 
to us in the early spring as the " peepers" of the swamps. They are among 
the earhest of the frogs to lay their eggs. During adult life they spend 
most of their time on the trunks of trees, where they receive immunity 
from attack because of their color markings. The feet of the tree toad are 
modified for climbing by having little disks on the ends of the toes, by 
means of which it is able to cling to vertical surfaces. 




Newt. From photograph loaned by the American Musexim of Natural History. 

Another common amphib'ian is the newt, a salamander. This smooth- 
skinned, four-limbed animal, often incorrectly called a lizard, passes its 
larval life in the water, where it breathes by means of external gills. Later 
it loses its gills, becomes provided with lungs, and comes out on land. 
Its coat, which was greenish in the water, changes to a bright orange 
color. In this condition we sometimes find newts crawhng on wood 
roads after a rain. After over two years' Ufe on land, it again returns 
to the water, becomes green with red spots (as seen in the Figure), and 



280 



THE VERTEBRATE ANIMALS 




Spotted salamander. From photograph loaned by 
the American Museum of Natural History. 



is able to reproduce its kind. Some salamanders never have lungs, but 

breathe through the moist skin. 

Still other amphibians are the nuid pup})ios, sirens or mud eels, and the 

axolotl. All of the amphibians differ from tlie reptiles in having a smootli 

skin with no scales, and 
in passing the early 
stage of their existence 
in the water. 

Characteristics of 
Amphibia. — The 
frog belongs to the 
class of vertebrates 
known as Amphibia. 
As the name indi- 
cates (ainphi, both, 
and hia, life), mem- 
bers of this group pass more or less of their life in the water, 
although in the adult state they are provided with lungs and can 
live on land. In the earlier stages of their development they 
take oxygen into the blood by means of gills. At all times, but 
especially during the winter, the skin serves as a breathing 
organ. The skin is soft and unprotected by bony plates or 
scales. The heart has three chambers: two auricles and one 
ventricle. Amphibians undergo metamorphosis during develop- 
ment. 

Order I. Urode'la. Amphibia having usuallj^ poorty developed appen- 
dages. Tail persistent through life. Examples: mud puppy, newt, 
salamander. 

Order II. Anu'ra. Tnilless Amphibia. Hind legs well developed. Exam- 
ples: toad and frog. 

Summary. — The frog is one of the most common of our 
amphibians and shows the characteristics of this group: (1) it 
passes part of its life in the water as a tadpole and part either in 
or out of the water in the adult state, (2) the skin is soft and 
provided with slime glands, (3) the animal breathes as an adult 
by means of lungs and skin but in the young stage by means of 
gills, (4) it passes through a metamorphosis characteristic of the 
group. 



REPTILES 281 

The group are of some economic importance in the destruc- 
tion of harmful insects (toad) and as food (frog). 

Problem Questions. — 1. How does a frog breatlie? catch 
food? jump? swim? 

2. Explain the steps in the metamorphosis of a frog and the 
adaptations of each step. 

3. How do the toads show amphibian characteristics? 

Problem and Project References 

Ditmars, The Bairachians of New York. Guide Leaflet 19, American Museum 

of Natural History. 
Dickerson, The Frog Book. Doubleday, Page, and Company. 
Herri ck, Textbook in General Zoology, Chap. XX. American Book Company. 
Hodge, Nature Study and Life, Chaps. XVI, XVII. Ginn and Company. 
Holmes, The Biology of the Frog. The Macmillan Company. 
Hunter, Laboratory Problems in Civic Biology. American Book Company. 
Morgan, The Development of the Frog's Egg. The Macmillan Company. 
Nature Study Leaflets, Cornell Nature Study, Bulletins XVI, XVII. 

Reptiles 

Reptiles differ from amphibians in that they always breathe 
by means of lungs. 

Turtles' Adaptations for Life. — The turtles form a large and 
interesting group, including both sea and land animals, the latter 
called tortoises. The body is flattened, and is covered on the 
dorsal and ventral sides by a bony frame- 
work. This covering is composed of plates 
cemented to the true bone underneath, the 
whole forming one big horny cover. This 
shell, an adaptation for protection, is re- 
markable in the box tortoise, where a hinge 
on the ventral side allows the animal to 
retreat within the shell, the head and legs 

being completely covered. Western painted turtle. 

Adaptations for Food Getting. — The 
long neck and powerful, horny jaws are factors in procuring 
food. Turtles have no teeth. Prey is seized and held by the 
jaws, the claws of the front legs being used to tear the food. 

Tiutles are very strong for their size. The stout legs carry the 

HUNT. NBW B8. — 19 




282 



THE VERTEBRATE ANIMALS 




Box tortoise. From photograph loaned by 
the American Museum of Natural History. 



animal slowly on land, and in the water, being slightly webbed, 
they are of service in swimming. In some water turtles the 
front limbs are modified into ilippers for swinuning. The strong 
claws are used for cUgging, especially at the egg-laying season, 
for some turtles dig holes in sandy beaches in which the eggs 
are deposited^ 

Some Different Turtles. — Turtles are mostly aquatic in habit. Among 
the exceptions are the box tortoise already mentioned and the giant tortoise 

of the Galapagos Islands. 
Many of the salt-water tur- 
tles are of large size, the 
leatherback and the green 
turtle often weighing six 
hundred to seven hundred 
pounds each. The flesh of 
the green turtle and es- 
pecially the diamond-back 
terrapin, an animal found 
in the salt marshes along 
our southeastern coast, is 
highly esteemed as food. 
Unfortunately for the preser- 
vation of the species, these animals are usually taken during the breeding 
season when they go to sandy beaches to lay their eggs. 

Lizards. — Lizards may be recognized by their long body with 
four legs of nearly equal size. The body is covered with scales. 
The animal never lives 
in water, it is active in 
habit, and it does not 
undergo a metamor- 
phosis. Lizards are 
generally harmless crea- 
tures, the Gila monster 
of New Mexico and 
Arizona, a poisonous 
variety, being one ex- 
ception. Lizards are of 
economic importance to 
man, because they eat insects and include the injurious ones in 
their dietary, The iguana of Central America and South 




The Gila jnonster. Photopjraph one tenth 
natural size, by Davison. 



REPTILES 



283 




America, growing to a length of three feet or more, has the dis- 
tinction of being one of the few edible lizards. 

Snakes. — Probably the most disliked and feared of all ani- 
mals are the snakes. This feeling, however, is rarely deserved, 
for, on the whole, our common snakes are beneficial to man. 
The black snake and the milk snake feed largely on injmious 
rodents (rats, mice, 
etc.), the pretty 
green snake eats 
injurious insects, 
and the little De- 
Kays snake feeds 
partially on slugs. 
If it were not that 
the rattlesnake and 
the copperhead are 
venomous, they also 

could be said to be useful, for they live on English sparrows^ rats> 
mice, moles, and rabbits. 

Snakes are ahnost the only vertebrates without appendages. 
Although the limbs are absent, the pelvic and pectoral girdles 
are developed. The very long backbone is made up of a large 
number of vertebrae, as many as four hundred being found in 
the boa constrictor. Ribs are attached to all the vertebrae in 
the region of the body cavity. 

Locomotion. — Locomotion is performed by pulling and push- 
ing the body along the ground, a leverage being obtained by 
means of the broad, flat scales, or scutes, with which the ventral 
side of the body is covered. Snakes may move without twist- 
ing the body. This is accomplished by a regular drawing for- 
ward of the scutes and then pushing them backward rather 
violently. 



A garter snake, one of our commonest harmless 
reptiles. 



Feeding Habits. — The bones of the jaw are very loosely joined to- 
gether. Thus the mouth of the snake is capable of wide distention. Id 
holds its prey by means of incurved teeth, two of which (in the poisonous 
snakes) are hollow or grooved, and serve as a duct for the passage of 
poison. The poison glands are at the base of the curved fangs in the 
upper jaw. The tongue is very iQng ^n4 cleit at the end. It is an organ 



284 



THE VERTEBRATE ANIMALS 



of touch and taste, and is not, as many people believe, u^ed as a sting. 

The food is swallowed whole, and pushed down by rhythmic contractions 

of the muscles surrounding the gullet. Snakes usually refuse other than 

living prey. 

Adaptations. — Snakes are not extremely proHfic animals, but hold their 

o^Ti with other forms of 
life, because of their 
numerous adaptations for 
protection, their noiseless 
movement, protective color, 
and, in some cases, by their 
odor and poison. 

Poisonous Snakes, — Not 
aU snakes can be said to be 
harmless. The bite of the 
rattlesnake of our own 
country, although dangerous, 
seldom kills. The dreaded 
cobra of India has a record 
of over two hundred and 
fifty thousand persons killed 

in thirty-five years. The Indian government yearly pays out large sums for 

the extermination of venomous snakes, over two hundred thousand of 

which have been kiUed during a single year. 

Alligators and Crocodiles. — Crocodiles are mostly confined to Asia 

and Africa, while alligators are natives of North and South America. 




Skull of boa coustrictor, two thirds natural 
size. Note the in-pointing teeth. Photograph 
by Davison. 




Young alligator. One fifth natural size. 



The chief structural difference between them is that the teeth in alligators 
are set in long sockets, while those of the crocodiles are not. Both of 
these Hzardlike animals have broad, vertically flattened tails adapted 
to swimming. The eyes and tip of the snout, the latter holding the nos- 
tril holes, protrude from the head, so that the animal may float motion- 



REPTILES 285 

less near the surface of the water with only eyes and nostrils visible. The 
nostrils are closed by a valve when the animal is under water. These rep- 
tiles feed on fishes, but often attack large animals, as horses, cows, and 
even man. They seek their prey chiefly at night, and spend the day bask- 
ing in the sun. The crocodiles of the Ganges River in India levy a yearly 
tribute of many hundred hves from the natives. 

Classification of Reptiles 

Order I. Chelo'nia (turtles). Flattened reptiles with body inclosed in 
bony case. No teeth or sternum (breastbone). Two pairs of limbs. 
Examples: snapping turtle, box tortoise. 

Order II. Lacertil'ia (Kzards). Body covered with scales, usually having 
two pairs of limbs. Examples : fence lizard, horned toad. 

Order III. Ophid'ia (snakes). Body elongated, covered with scales. No 
hmbs present. Examples: garter snake, rattlesnake. 

Order IV. Crocodil'ia. Fresh-water reptiles with elongated body and 
bony scales on skin. Two pairs of limbs. Examples alligator, croco- 
dile. 

Summary. — Turtles, lizards, and snakes belong tc the class of 
v^ertebrates known as ReiptU'ia. Such animals are characterized 
by having scales developed from the skin, which in the turtle 
have become bony and are connected with the internal skeleton, 
forming a shell. Reptiles always breathe by means of lungs, 
differing in this respect from the amphibians. They show their 
distant relationship to birds in that their large eggs are incased 
in a leathery, limy shell. 

In general reptiles are useful either as food (turtles) or as 
destroyers of harmful animals. Most snakes are useful, although 
the poisonous snakes and crocodiles still take a yearly toll of 
deaths in some parts of the world. 

Problem and Project References 

Davison, Practical Zoology, pages 211-226. American Book Company. 
Ditmars, The Reptiles of New York. Guide Leaflet 20, American Museum of 

Natural History. 
Ditmars, The Reptile Book. Doubleday, Page, and Company. 
Jordan, Kellogg, and Heath, Animal Studies, Chap. XVI. D. Appleton and 

Company. 
Riverside Natural History. Houghton, Mifflin, and Company. 



286 



THE VERTEBRATE ANIMALS 



Birds 

Problem. To study some adaptations in birds. (Laboratory 
Manual, Prob. XXXIX; Laboratory Problems: Prob. 118.) 

Adaptations for Life. — Birds are distinguished from all other 
animals by their covering of feathers and by the peculiar modifi- 
cation of the fore Hmb into a wing for flight. Hollow bones, 
feathers, and air spaces inside of the bod}'- cavity make them 
light for staying up in the air. The body is boat-shaped and 
pointed at the anterior end. The tail acts as a rudder. Tlie 

LOWER MANDIBLE 



TAIL COVERTS 



CO/fffTJ 




tfJNDTOE 



y^^^TOES 



Diagram of a bird. 

bill is horny and adapted for securing food. The legs show great 
variations for running, perching, swimming, and scratching. 

Field Work. — Bird activities may best be studied out of doors. A city 
park offers more or less opportunity for such study, for several of our 
nat?ve birds make the parks their home. If not these, then the English 
sparrow can be studied as it is found everywhere in the East. The best 
time for making observations is early in the morning, especially in the 
spring season. 

Adaptation of the Wing. — The wing is a modified arm, with 
the fingers very much reduced. It consists of a few long bones 



BIRDS 



287 



and a few small muscles, covered with skin. To the posterior 
edge of the wing are fastened long quill feathers which overlap 
and make a broad, stiff surface for pressing against the air. The 
wing is jointed and moves up and down in flight. Powerful 
breast muscles are attached to the 
wing bones and give great strength 
in movement. The wings fold against 
the side of the body when at rest. 
Watch a bird in flight. The rate of 
movement of the wing differs greatly 
in different birds. The wing of a bird 
is slightly concave on the lower sur- 
face when outstretched. Thus on 
the downward stroke of the wing 
more resistance is offered to the air. 
Birds with long, thin wings, as the 
hawks and gulls, move their wings in 
flight with much less rapidity than 
those with short, wide wings, as the 
grouse or quail. The latter birds 
start with much less apparent effort 
than the birds with longer wings; 
they are, however, less capable of 
sustained flight. 

Feathers. — Few people reahze 
that the body of a bird is not 
completely covered with feathers. 
Featherless areas can be found on the 
body of any common bird, although 
tiny '^pin feathers'' are found on 
such areas as well as on other parts 
of the body. Soft down feathers 
on the body make a covering for warmth. Larger feathers give 
the rounded contour to the body. In the wings we find quill 
feathers; these are adapted for service in flight by having long 
hollow shafts, from which lateral interlocking branches are given 
off, the whole making a light structure and offering consider- 
able resistance to the air. Feathers are developed from the 




Feathers of a meadow lark. 
Which of the above are used 
for flight? How do you know? 
From photograph loaned by 
the American Museum of 
Natural History. 



288 



THE VERTEBRATE ANIMALS 



outer layer of the skin, and are formed in almost exactly the 
same manner as are the scales of a fish or a Uzard. The first 
feathers developed on the body are evidently for protection 
against cold and wet, but later in life they serve other uses 
as well. The feathers of most male birds are brightly colored. 
This seems to make them attractive to the females of the 
species; thus the male may win its mate. 

Adaptations of the Legs. — The ankle of a bird is long and 
reptile-like and is covered, hke the foot, with scales. The most 
extraordinary adaptations are found in the feet of various birds 




Adaptation in feet of birds: 1, swift (clinging); 2, ouzel (perching); 3, wood- 
pecker (climbing); 4, pheasant (scratching); 5, hawk (seizing prey); 6, ostrich 
(limning) ; 7, duck (swimming) ; 8, grebe (diving) ; 9, avocet (wading) ; 10, stork 
(wading). In each case can you make out the way in which the bird's foot i& 
adapted to do its work? 

some for perching, others for swimming, others for wading, etc. 
We are able, by looking at the feet of a bird, to decide almost 
certainly its habitat, method of life, and perhaps its food. 

In the perching birds we find three toes in front and one behind, 
the hind toe playing an important part in clinging to the perch. 
In swallows, rapid and untiring flyers, the feet are small. In 
the case of the parrots, where the foot is used for holding food, 
climbing, and cUnging, we find the four-clawed toes arranged 



BIRDS 



289 



Cervical Vertebr9 



Pelvic Qirdle 
Tall 



FingerBones 

Sterrim 



two in front and two behind. Hawks and eagles are provided with 
strong curved talons with which the prey is seized and killed. 

Adaptation for semiaquatic life is seen in plovers, herons, or 
storks, where long legs and 
long toes enable the birds 
to seek their food in soft 
mud among reeds or lily 
pads, or along sand flats. 
True aquatic birds, on the 
other hand, are provided 
with webbed toes. The 
foot of the common barn- ^°"^^^^"^ 
yard duck, for example, is 
much like that of the alli- 
gator. In the ostrich and 
cassowary the wings are 
small and not used for 
flight; the legs are long and 
powerful and fitted for 
rapid running. 

Perching. — The method 
of perching is an interest- 
ing one. The three toes 
in front ciurve around the 
perch, often meeting the 
posterior toe, which is curved also. The tendons of the leg 
and foot are self locking, and such birds are held in place as 
perfectly when asleep as when awake. A part of the ear, known 
as the semicircular canals, has to do with the function of bal- 
ancing. In the flamingoes and other birds, which do not perch, 
balancing appears to be automatic; thus the bird is able to 
maintain an upright position even when asleep. 

Tail. — The tail is sometimes used in balancing; its chief 
function, however, appears to be that of a rudder during flight. 
Most birds have under the skin of the tail a large oil gland, 
whence comes the supply of oil that is used in waterproofing 
the feathers when they preen themselves. 

The Skeleton. — The skeleton combines lightness, flexibility, 




Fusedbones 
ofankle 



2ndTo 
JrdToe - 

4thToe-^ 

Skeleton of a fowl. 



290 



THE VERTEBRATE ANIMAI^S 



and strength. Many bones are hollow or have large spongy 
cavities. The bones of the head and neck show many and 
varied adaptations to the life the bird leads. The vertebrae 
which form the framework of the neck are strong and flexible. 
They vary in shape and in number. The swan, seeking its 
food under water, has a neck containing twenty-three long 
vertebrae; the English sparrow, in a different environment, 
has only fourteen short ones. Some bones, notably the breast- 
bone, are greatly developed in flying birds for the attachment 
of the muscles used in flight. 




Adaptations in the bills of birds. Could we tell anything about the food of a 
bird from its bill? Do these birds get their food in the same manner? 1, shoe- 
bill; 2, hawk; 3, bunting; 4, thrush; 5, flamingo; 6, spoonbill; 7, pelican; 8, duck; 
9, pigeon; 10, toucan; 11, bird of pai'adise; 12, swift; 13, skimmer; 14, stork. 



Bill. — The form of the bill shows adaptation to a wonderful 
degree, varying greatly according to the habits of the bird. A 
duck has a flat bill for pushing through the mud and straining 
out the food; a bird of prey has a curved or hooked beak for 
tearing; the woodpecker has a sharp, straight bill for piercing 
the bark of tref^s in search of the insect larvae underneath. 

Birds do not have teeth. The edge of the bill may appear 
to be toothed, as in some fish-eating ducks; however, the projec- 
tions are not true teeth. Frequently the tongue has sharp. 



BIRDS 291 

toothlike edges which serve the same purpose as the recurved 
teeth of the frog or snake. 

Adaptations for Active Life. — The rate of respiration, of 
heartbeat, and the body temperature are all higher in the bird 
than in man. 

These are among the greatest adaptations to the active life 
led by a bird. Man breathes sixteen or eighteen times a minute. 
Birds breathe from twenty to sixty times a minute. The lungs 
of a bird are not large. Its bronchial tubes are continued 
through the lungs into hollow spaces filled with air, which are 
found between the organs of the body. Only the lungs, how- 
ever, are used for breathing. Because of the increased ac- 
tivity of a bird, there comes a necessity for a greater supply 
of oxygen, an increased blood supply to carry the material 
to be oxidized in the release of energy, and a means of rapid 
excretion of the wastes resulting from the process of oxidation. 
A bird may be compared to a high-pressure steam engine; in 
order to release the energy which it uses in flight, a large 
quantity of fuel which will oxidize quickly must be used. Birds 
are large eaters, and the digestive tract is fitted to digest the 
food quickly. As soon as the food is absorbed by the blood, it 
may be sent rapidly to the places where it is needed, by means 
of the strong four-chambered heart and large blood vessels. 

The high temperature of the bird is a direct result of this 
rapid oxidation; furthermore, the feathers and the oily skin 
form an insulation which does not readily permit the escape 
of heat. This insulating cover is of much use to the bird in its 
flights at high altitudes, where the temperature is often very 
low. 

The Nervous System and the Senses. — The central nervous system 
is well developed. A large forebrain is present, which, according to a series 
of elaborate experiments with pigeons, is found to have to do with the 
conscious life of the bird. The cerebellum takes care of the acts which are 
purely mechanical. 

Sight is probably the best developed of the senses of a bird. The keen- 
ness of vision of a hawk is proverbial. It has been noticed that in a bird 
which hunts its prey at night, the eyes look toward the front of the face. 
In a bird which is hunted, as in the dove, the eyes are placed at the sides 
of the head. In the case of the woodcock, which feeds at night in the 



292 



THE VERTEBRATE ANIMALS 



■ 1 






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1""***- 










^ •"£?_* 




^>^>^ Wi IBIIfp'^'' ^-^^ 




1 


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^^ 


i^^ 


y 








H^^H 




W^^^^SM 


HhBn 


iJi 


^J^^^^^M 






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marshes, and which is in constant danger from attacks by owls, the eyes 
have come to he far back on the top of the head. Hearing is also well 
developed in most birds, as may be demonstrated with any canary. 

The sense of smell does not appear to be well developed in any bird, and 
is especially deficient in seed-eating birds. 

Nesting Habits. — Among the most interesting of all instincts 
shown by birds are those of nest building. Some invertebrates, 

as spiders and ants, pro- 
tect the eggs when laid. 
In the vertebrate group 
some fishes (as the sun- 
fish and stickleback) 
make nests for holding 
the eggs. But most fishes, 
and indeed nearly all 
other vertebrates lower 
than the birds, leave the 
eggs to be hatched by the 
heat of the sun. Birds 

Nest of a phcebe under a barn floor. • i, x xt_ • J.^ i. 

mcubate their eggs, that 
is, hatch them, by the heat of their bodies. Hence a nest, 
in which to rest, is needed. The ostrich is an exception; 
it makes no nest, but lays its eggs on the ground ; then the male 
and the female take turns 
in sitting on them. Such 
birds as are immune from 
the attacks of enemies be- 
cause of their isolation or 
their protective coloration 
(as the puffins, gulls, and 
terns), build a rough nest 
among the rocks or on the 
beach. The eggs, espe- 
cially those of the tern, are 
marked and colored so as 
to be almost indistinguish- 
able from the rocks or sand on which they rest. Other birds have 
made their nest a home and a place of refuge as well as a place 




Common tern and young, showing nest- 
ing and feeding habits. From group at the 
American Museum of Natural History. 



BIRDS 



293 




,»tmi^^mmmm 



to hatch the eggs. Such are the nest of the woodpecker in a 
hollow tree and the hanging nest of the oriole. Some nests 
which might be easily seen because of their location are often 
rendered inconspicuous by the builders; for example, the lichen- 
covered nest of the humming birds. 

Care of the Young. — After the eggs have been hatched, the 
young in most cases are quite 
dependent upon the parents 
for food. Most young birds 
are prodigious eaters; as a 
result they grow very rap- 
idly. It has been estimated 
that a young robin eats two 
or three times its own 
weight in worms every day. 
Many other young birds, 
especially kingbirds, are 
rapacious insect eaters. In 
the case of the pigeons and 

some other birds, food is Nest ol the chimney swift. 

swallowed by the mother, partially digested in the crop, and 
then regurgitated into the mouths of the young nestlings. 

Problem. How birds are of economic importance. (Lahora" 
tory Manual, Proh. XL; Laboratory Problems, Probs. 121, 122.) 

Geographical Distribution and Migrations. — Most of us are 
aware that some birds remain in a given region during the 
whole year, while other birds appear with the approach of 
spring, and depart southward with the warm weather in the 
fall of the year. Such birds we call migrants, while those that 
remain in one place the year round are called residents. 

In Europe, where the problem of bird migration has been 
studied carefully, migrations appear to take place along well- 
defined paths. These paths usually follow the coast very ex- 
actly, although in places they may take the line of coast 
that existed in former geological times. In this country the 
Mississippi valley, a former arm of the sea, forms one line of 
migration, while the north Atlantic seacoast forms another route. 



294 



THE VERTEBRATE ANIMALS 



It has been shown that the southern movement of migratory 
birds in the fall of the year is not due entirely to the advent of 
cold weather, but i^ largely a matter of adjustment to food 
supply. A migrant almost always depends upon insects, fruits, 
and grains for the whole or a large part of its food. Most 
winter residents, as the crow, are omnivorous in diet. Others, 
as the English sparrow, may be seed eaters, but under stress 
change their diet to almost anything in the line of food; still 
others, as the woodpeckers, although insect-eating birds, man- 
age to find the desired food tucked away under the bark of 
trees. Many insect-eating birds, however, because their food 
is found on green plants, appear to be forced southward by 
the cold weather. 

Food of Birds. — Birds are of tremendous economic impor- 
tance to our country and a very great help to agriculture because 

a large part of their diet includes 
insects harmful to vegetation, 
and the seeds of weeds, enemies 
also of the farmer. Birds hke 
the crow and robin feed at times 
upon fruit and grain and at other 
times upon insects. So grateful 
were the early settlers in Utah to 
the seagulls for dehvering them 
from a plague of ''crickets" (per- 
haps locusts), that they erected 
a beautiful monument to the 
seagulls. A plague of insects 
threatened to destroy the crops 
and the people were in despair, 
when along came crowds of sea- 
gulls that ate the pests and 
saved the crops. 

Not all birds are seed or 
insect feeders. Some, as the 
cormorants, ospreys, and terns, are active fishers. Near large 
cities gulls act as scavengers, destroying much floating garbage 
that otherwise might be washed ashore to become a menace to 




Food of some common birds. 



BIRDS 295 

health. Sea birds also live upon shellfish and crustaceans (as 
small crabs, shrimps, etc.); some even eat lower organisms. 
The kea parrot, once a fruit eater, now takes its meal from the 
muscles forming the backs of living sheep. Birds of pre}^ (owls 
and hawks) eat smaller birds and mammals, including many 
rodents; for example, field mice, rats, and other pests. 

Common Birds. — The following pages will help one to recog- 
nize a few of our common birds which are of decided economic 
value or harm. The size, color markings, food, and familiar 
habits of some of our common birds will be given, with a brief 
statement of the reason why they are man's friends or enemies. 
• Robin. — A bird known to all of us makes an excellent type 
for comparison with other less known birds. The robin is 9 to 
10 inches long. The male is dark gray above tinged with olive, 
brown on the wings, and black on the head and tail; the throat 
is light gray with black spots, and the breast is red. The fe- 
male is similar but darker in color. The robins live near houses 
and in orchards and make their nests of grass and mud, in trees 
or on buildings. The robin is a true thrush, whose pleasing 
song dehghts us in early Spring. Its economic position is often 
discussed as it eats much fruit early in the season. Ordinarily 
its diet consists of about 40 per cent 
insects, most of which, as ground 
beetles, caterpillars, plant Hce, and 
cutworms, are harmful. It eats earth- 
worms, also, which are useful to the 
farmer. 

Bluebird. — One of our earliest mi- 
grants. Its cheery note and blue coat 
are easily recognized. It is Gf to 7 
inches in length. The male is bright Biuebi-d. 

blue above, and chestnut iinderneath. The female is duller in 
color. It nests in holes in trees or posts and in bird houses. 
Its food consists largely of grasshoppers with a few beetles, 
spiders, and caterpillars. 

Song sparrow. — Another of our earliest visitors. The male 
is about 6i inches long, brown above, head reddish-brown 
mottled with blackish streaks. A streak of gray runs through 




296 



THE VERTEBRATE ANIMALS 



the center of the crown, and there is a characteristic black line 
through the eye and two on the throat. The breast is spotted 
on a white ground. Its nest is usually on the ground or in a 
bush. It is a friendly bird and is often seen near houses, though 
it prefers moist areas farther away from man. It eats some 
insects, but like most of the native sparrows it feeds mainly 
upon weed se^ds. 

Chickadee. — A smaller bird, about 5J inches in length. It 
is often an all-year-round resident. The crown of the head 
and throat are black, the cheeks white, the back gray, and 
the belly often a dirty white. It feeds upon spiders, plant 
lice, and other insects, and in the winter time devours large 
quantities of eggs laid by these pests, one bird eating more 
than 430 eggs in a single day. It is certainly one of man's 
best bird friends. 

House Wren. — This little migrant nests around our homes, 
is a great songster and a decided asset to us, because of its 
varied diet of cutworms, spiders, weevils. May flies, etc. It has 
been estimated to catch 600 insects a day. It is a friendly little 
bird whose worst enemies are English sparrows and cats. A 
proper nesting box with a small entrance is one of its best 
means of protection. The house wren is not quite 5 inches long. 
The upper part is brown, the lower grayish brown and white. 
The wings, flanks, and tail are slightly barred. It can be recog- 
nized easily by its small size, 
coloring, incessant singing or 
chattering, and by the fact 
that its tail is frequently held 
erect when at rest. 

American Goldfinch. — This 
bright yellow songster is one 
of our most attractive birds. 
It is often called the wild 
canary. It is a little over 5 inches long. The male has a 
bright yellow body with a black cap and black markings on 
tail and wings-. The female is a deep brown. The goldfinch 
eats seeds of weeds, preferring those of the dandelion and thistle, 
two of our greatest weed pests. 




American goldfinch. 



COMMON BIRDS 



297 



I 



Yellow Warbler. — A bird often confused with the goldfinch 
is the yellow warbler. Like all warblers, this is a small bird; 
it is about 5 inches in length. Its color is yellow, flecked 
with olive or brown (note it has no black on the head as does 
the goldfinch). It nests near houses in low trees or bushes. 
It is of much economic importance because of its preference for 
the browntail and gypsy moth caterpillars, and other enemies 
of the forest trees. We are spending millions of dollars every 
year to fight these imported pests, and the goldfinch may help 
turn the scale against them if it is protected and encouraged to 
nest near our homes. What can you do to help? 

Phoebe. — Another tireless hunter of insect pests is the phoebe. 
This bird is a flycatcher, seizing insects on the wing. It builds 
a nest of mud — often under old bridges, around barns, or some- 
times under a barn floor (p. 292). Its food consists of browntail 
and gypsy moths, cankerworms, beetles, and flies. The phoebe is 
about 7 inches long, dusky olive-brown above, yellowish white 
underneath, wings and tail dusky. The head is slightly crested, 
bill and feet are black. It is one of our early visitors. 

Barn Swallow. — Another bird with nesting habits similar to 
those of the phoebe is the barn swallow, which makes a nest 
plastered to the rafters of a 
barn or outbuilding. While 
most birds decrease in num- 
ber with the cutting of 
forests and the building of 
cities, the barn swallow has 
increased because it feeds on 
insects which live on crops 
in cleared fields. It eats 
moths of cutworms, codling 
moths, and leaf cutters, with 
many others of the farmer's 
insect enemies. This swallow 
is between 6 and 7 inches in length. It is dark blue above, with 
forehead, throat, and upper breast chestnut; the lower breast 
and belly buff. The tail is deeply forked, showing white mark- 
ings when spread. 

HUNT. NEW E8. — 20o 




Barn swallows. 



298 



THE VERTEBRATE ANIMALS 



Catbird. — Another bird which nests near houses and prefers 
the company of man is the catbird. From early May to late 
October its various calls and songs are the delight of all bird 
lovers, for it is a great mimic and somewhat of a tease. The cat- 
bird, although it eats much fruit, is largely an insect feeder and 
gives its young 95 per cent insect food. It is an enemy to 
caterpillars, especially the cutworm. It is about 9 inches in 
length, and of a dark grayish color, with the top of ^ head and 
the tail blackish. 

Downy Woodpecker. — The woodpeckers are famiUar to most 
boys and girls because of their conspicuous color and their 
peculiar habits. The downy woodpecker is 6J inches long, 
black and white barred, with a small patch of scarlet at the 
top of the head. It runs quickly up and down the trunks of 
trees, tapping the wood to locate insect holes. The bill is 
strong, sharp at the end, and is used as a chisel in boring 
into wood. The tongue is spearlike, 1 to 1§ inches long, and is 
used to pull out the larvae which it seeks. Its chief food is larvae 

of maple, birch, apple and other 
borers. Woolly aphids, caterpillars, 
and crysalids are also its prey. 
A woodpecker has been observed 
to work over 180 trees in 2 J hours' 
time. In some cases a downy 
woodpecker is found which lives 
up to its name of sapsucker, but 
the good done b3^ these little birds 
far outweighs the harm done by 
them. 

Flicker. — This bird is not a 
typical woodpecker although it has 
similar habits. It is a large bird 
12 inches long. The male is brown 
above and golden yellow below, 
with black markings, and a scarlet 
crescent across the neck. It has a white rump which is con- 
spicuous in flight and makes an easily recognized mark. The 
flicker is generally useful, feeding upon plant lice, ants (which 




Flicker. 



COMMON BIRDS 



299 



make up about 45 per cent of its food), grasshoppers, caterpillars, 
and weed seeds. Like the woodpecker, it nests in hollow trees. 

Baltimore Oriole. — This bright-colored and attractive bird 
is about 7J inches long. The male has the upper back and 
throat black with the outer tail feathers, breast, and under parts 
orange. The female is not so brilHantly colored, having a yellow 
instead of orange color. The hanging nests of the oriole, often 
woven with bits of string and other materials, are a common 
sight in elm trees near our homes. These birds prefer inhab- 
ited areas and, because of their protected nests, are on the in- 
crease in spite of cats and the English sparrow. They feed 
largely upon the cankerworm, tussock, browntail, and forest 
tent caterpillars. 

Screech Owl. — This is a small owl and one of the most useful, 
as it feeds upon field mice and other small 
destructive rodents as well as upon some 
moths, caterpillars, and beetles. It is about 
as large as a quail, or 9i inches in length. 
" Its general coloring is gray on the under 
parts and reddish brown above. The eye 
is yellow. It usually nests in hollow trees. 

Crow. — Our common crow, a glossy black 
bird from 16 to 17J inches long, is one of the 
few birds that may do more harm than good. 
In the early spring the crow is useful and 
eats insect larvae, such as cutworms and 
May beetle larvae, and field mice, but 
later it does much harm in the newly 
planted corn fields. The crow is accused 
of stealing young chickens, ducks, and turkeys, and the eggs 
and young of many useful birds. 

English Sparrow. — The English sparrow is an example of a 
bird introduced for the purpose of insect destruction, that has 
done great harm because of its relation to our native birds. 
Introduced at Brooklyn in 1850 for the purpose of exterminat- 
ing the cankerworm, it soon abandoned an insect diet to a large 
Extent in favor of one of grain and has driven out many of 
our native insect feeders. Investigations by the Department of 




Screech owl. 




300 THE VERTEBRATE ANIMALS 

Agriculture show that in the country these birds and their j^oung 
feed to a large extent upon grain, thus showing them to be injuri- 
ous to agriculture. Dirty and very prolific, the}^ long since worked 

their way from the East as far as the 
Pacific coast. In this area the blue- 
bird, song sparrow, and yellowbird 
have all been forced to give way, 
as well as many larger birds of great 
economic value and beauty. The Eng- 
lish sparrow has become a national 
pest, and should be exterminated 
in order to save our native birds. 
^^^^'^^^^ It is feared in some quarters that the 

English starling, which has recently 
Cooper's hawk. been introduced into this country, 

may in time prove a pest as formidable as the English sparrow. 
Birds Harmful to Man. — Wliile there are a few birds that do 
both harm and good Hke the crow and the robin, there are 
others that are bad and we can find little or no good to say 
about them. The English sparrow is the greatest bird pest, for 
reasons given above. The cowbird never builds a nest nor cares 
for her young. She lays her eggs in the nests of smaller birds, 
where later the young cowbirds cause the death of the rightful 
inhabitants of the nest. Cooper's hawk, the sharp-shinned hawk, 
and the great horned owl kill smaller, beneficial birds. The 
beautiful belted kingfisher sits in a tree beside the rivers and 
fishes, eating aquatic insects, mice, frogs, and grasshoppers also. 
Fortunately there are very few birds to put on the black Ust. 
Extermination of our Native Birds. — ^Yithin recent times has 
been witnessed the almost total extermination of some species 
of our native birds. The American passenger pigeon, once very 
abundant in the Middle West, is now practically extinct. To- 
day not a single specimen of this pigeon can be found, because 
they were slaughtered by the hundreds of thousands during the 
breeding season. The wholesale killing of the snowj^ egret to 
furnish ornaments for ladies' headwear is another example of 
the impro\'idence of our feUow countrymen. The EngHsh spar- 
row and wholesale killing of birds for plumage, eggs, and food, 



COMMON BIRDS 301 

and often for mere sport, caused the decrease of our birds to 46 
per cent in thirty states and territories within fifteen years. 
Laws made by state and national governments have done much 
to protect the birds and check their rapid decrease. Places of 
refuge or sanctuaries where birds are undisturbed during the 
nesting season have saved the lives of many hundreds. Societies 
and clubs have aroused interest all over the country and now 
many boys and girls as well as older people are watching, feed- 
ing, and protecting birds in every possible way. The effect of 
killing native birds is now seen in Italy and Japan, where insect 
pests are increasing. We should aU do our part in preventing 
the loss of our native birds here, not only because of their 
beauty and their song, but also because of their very great 
economic importance. 

Relationship of Birds and Reptiles. — The birds afford an 
interesting example of how the history of past ages of the earth 
has given a clue to the structural relation which birds bear to 
other animals. Several years ago, two fossil skeletons were 
found in Europe of a birdlike creature which had not only wings 
and feathers, but also teeth and a lizardlike tail. From these 
fossil remains and certain structures (as scales) and habits (as 
the egg-laying habits), naturahsts have concluded that birds 
and reptiles in distant times were nearly related and that our 
existing birds probably developed from a reptile-like ancestor 
many ages ago. 

Classification of Birds 

Division I. Rati'toe. Running birds without keeled breastbone. Exam- 
ples: ostrich, cassowary. 
Division II. Carina' tee. Birds with keeled breastbone. 

Order i. Pas' seres. Perching birds; three toes in front, one behind. 

One half of all species of birds are included in this order. Examples: 

sparrow, thrush, swallow. 
Order ii. Galli'nce. Strong legs; feet adapted to perching. Bealj 

stout. Examples: jungle fowl, grouse, quail, domestic fowl. 
Order hi. Rapto'res. Birds of prey with hooked beak and strong claws. 

Examples: eagle, hawk, owl. 
Order iv. Grallato'res. Waders. Long neck, beak, and legs. Shore and 

water-loving birds. Examples: snipe, crane, heron. 
Order v. Natato'res. Divers and swimmers. Legs short, toes webbed. 

Examples: gull, duck, albatross. 



302 THE VERTEBRATE ANIMALS 

Order vi. Colum'bce. Like Gallinae, but with weaker legs. Examples: 
dove, pigeon. 

Order vii. Pica'riae. Woodpeckers. Two toes point forward, two back- 
ward, an adaptation for climbiQg. Long, strong bill. Examples: 
Downy and hairy woodpeckers. 

Summary. — Birds are feathered vertebrates with the anterior 
appendages fitted for flying. Adaptations for food getting are 
numerous and well shown in the different types of beaks 
and claws. 

Our native birds are of great economic importance because of 
their feeding habits, as follows: (1) They eat insects which 
destroy crops, injure trees, and are pests in many ways; ex- 
amples, the house wren, phoebe, and downy woodpecker. (2) 
They eat seeds of weeds, which if allowed to grow would give 
.the farmer much trouble; examples, sparrows, goldfinch, and 
pigeon. (3) They kill harmful rodents, as field mice and moles; 
example, screech owl. (4) They act as scavengers; example, the 
herring gull. 

Only a few birds are harmful, as indicated below: (1) They 
eat grain and fruit; examples, the crow and the robin. (2) 
They catch fish; example, the kingfisher. (3) They dig deep 
holes in trees and allow the sap to run out;, example, the sap- 
sucker. (4) They drive out and harm useful birds; examples, 
the English sparrow and some hawks. 

As the benefit received from birds is tremendous and the harm 
is very slight, we should do all that we can to protect and 
encourage these feathered neighbors. 

Problem Questions. — 1. What are the characteristics of a bird? 

2. Name some bird adaptations for food getting, for nest 
making, and for protection. 

3.' Discuss the food habits of ten useful birds found in your 
locality. 

4. Name five birds that are of doubtful economic importance 
and give the reasons for your answer. 

5. Classify each of the above-named birds according to the 
simple classification at the end of the section on birds. 

6. Explain how the food of birds determines their migrations. 

7. Why are birds considered related to reptiles? 



MAMMALS 303 

Problem and Peoject References 

Apgar, Birds of the United States. American Book Company, 

Beebe, The Bird. Henry Holt and Company. 

Blanchan, Bird Neighbors. Doubleday, Page, and Company. 

Chapman, Bird Life. D. Appleton and Company. 

Forbush, Useful Birds and their Protection. Mass. State Board of Agriculture. 

Hornaday, Our Vanishing Wild Life. New York Zoological Society. 

Hunter, Laboratory Problems in Civic Biology (for bibliography). American 
Book Company. 

Hunter and Whitman, Civic Science. American Book Company. 

Ward and T> &axbovn. Birds in their Relation to Man. J. B, Lippincott Company. 

Bulletins of U. S. Dept. of Agriculture, Div. of Biological Survey, Farmers' Bul- 
letins 54, 383, 506, and other Nature Study Leaflets XXII, XXIII, XXIV, 
XXV, Cornell Nature Study Bulletins, Publications of the Audubon 
Society. 

Mammals 

Mammals. — Dogs and cats, sheep and pigs, horses and cows, 
many other animals covered with hair, and man himself, have 
struct'.iral characteristics which cause them to be classed as mam- 
mals. Mammals, like some other vertebrates, have lungs and 
warm blood. UnHke all other vertebrates, however, they have a 
hairy covering and bear young developed to a form similar to 
their own,^ which they nurse with milk secreted by glands known 
as the mam'mary glands; hence the term " mammals." Mammals 
are considered the highest of vertebrate animals, not only be- 
cause of their complicated structure, but because of their 
mental development. 

Adaptations in Mammalia. — Of the thirty-five hundred spe- 
cies of mammals, most inhabit continents; a few species are 
found only on islands; and some, as the whale, inhabit the ocean. 
They vary in size from the whale and the elephant to the tiny 
shrew mice and moles. Adaptations abound; the seal and whale 
have the limbs modified into flippers, the sloth and squirrel have 
limbs peculiarly adapted to climbing, while the bats have the 
fore limbs modeled for flight. 

Carnivora. — As the word '^carniv'ora" denotes, carnivorous 
mammals are to a large extent flesh eaters. In a wild state 
they hunt their prey, which is caught and torn with the aid of 
well-developed claws and long, sharp teeth. These teeth, so 

^With the exception of the monotremes. 



304 



THE VERTEBRATE ANIMALS 



well developed in the dog, are known as canine teefch or dog 
teeth. All flesh-eating mammals are wandering hunters in a 
state of nature; many, as the bear and lion, have homes or dens 
to which they retreat. Some (for example, bears and raccoons) 

live part of the time upon berries 
and fruit. Seals, sea Hons, 
whales, and walruses are adapted 
to a life in the water; and their 
hind limbs are almost useless on 
land. Some of the fur bearers, 
as the otter and mink, lead a 
partially aquatic life. Others in 
this great group prefer regions of 
comparative dryness, as the inhabitants of the South African 
belt. A few, like the raccoon, live most of their time in the 
trees. Many have adaptations for food getting and escape 
from enemies; the seasonal change in color of the weasel is an 
example of an adaptation which serves both of the above pur- 
poses. This is only one of hundreds that might be mentioned. 




SkuU of dog. 




California sea lion. Photographed in the Philadelphia 
Zoological Gardens by Davison^ 

Economic Importance. — The Carnivora as a group are of 
much economic importance as the source of most of our fur. 
The fur seal fisheries alone amount to many millions of dollars 
annually. Otters, skunks, sables, weasels, and minks are of con- 
siderable importance as fur producers. Our domestic cats are 



MAMMALS 



305 



such factors in the extermination of our native birds that their 
place as house pets is seriously questioned by some people. 
Homeless cats are great hunters of birds and a general nuisance 
and should not be allowed to exist. In India, tigers, and in 
Africa, lions, are man-eating in certain locahties, and in our 
own country wolves, pumas, and wild cats do some damage. 

Rodents. — Mammals known as rodents have the teeth so 
modified that on both upper and lower jaws two prominent incisor 
teeth can be used for 
gnawing. These teeth 
keep their chisel-like 
edges because the 
back part of the teeth 
is softer and wears 
away more rapidly. 
The canine or dog 
teeth are lacking. We 
are all familiar with 
the destructive gnaw- 
ing quahties of one of 
the commonest of aU 
rodents, the rat. The 
common brown rat 




Skull of a porcupine, a rodent. Notice the large 
overlapping incisor teeth. Compare them with 
the teeth of a dog (see page 304). 



is an example of a manmial which has followed in man's foot- 
steps all over the world, doing him harm. Starting from 

China, it spread to Europe, 
and in 1775 it had obtained a 
lodgment in this country. In 
seventy-five years it reached the 
Pacific coast, and is now fairly 
common all over the United 
States, being one of the most pro- 
lific of all mammals. Tt is esti- 
mated that the rat causes a 
property loss of at least $200,- 
000,000 annually. A determined 
effort is being made to exterminate this pest because of its 
connection with bubonic plague. 




Beaver. Copyright, 1900, 
Radcliffe Dugmore. 



by A. 



306 



THE VERTEBRATE ANIMALS 




Although most rodents may be considered as pests (as the 

rat and mouse) others are of use to man. Some of them 

furnish food, as the rabbits, hares, and squirrels. Rabbits, 

although rapid breeders, 
are kept in check in most 
parts of this country by 
their natural enemies, 
birds of prey and flesh- 
eating mammals. But in 
Australia, where they 
were introduced by man, 
they have become so 
numerous that the Gov- 
ernment gives a bounty 
for their destruction. 
Thousands of sheep are 
starved to death each 
year because rabbits eat 
their pasturage. The fur 
of the beaver, one of the 

largest of this order, is of considerable Value, as are the coats 

of several other rodents. The fur of the rabbit is used in the 

manufacture of felt hats. 

The quills of the porcu- 
pines (greatly developed 

and stiffened hairs) have 

a slight commercial 

value. 

Ungulates: Hoofed 

Mammals. — This group 

includes most of the 

domesticated animals, as 

the horse, cow, sheep, 

and pig. Many of this 

group of animals came 

under the subjugating influence of man and now they form an 

important part of the world's wealth. 

The order of ungulates is a very large one. It is characterized 



Virginia deer. From photograph loaned by 
the American Museum of Natural History. 




The bison. 



MAMMALS 



307 



by the fact that the nails have grown down and become thickened 
as hoofs. In some cases only two (the third and fourth) toes are 
largely developed. Such animals have a cleft hoof, as the ox, 
deer, sheep, and pigs. They are the even-toed ungulates. The 
deer family contains the largest number of species and indi- 
viduals among our native forms, and in fact the world over. 
Among them are the common Virginia deer of the Eastern 
states, the white-tailed deer of our Adirondack forests. The 
bison, or buffalo, is nearly related to the deer and wild cattle. 
Formerly bisons existed in enormous numbers on our Western 
plains. They were often hunted by whites and Indians for the 
hides and tongues only, and thousands of carcasses were left 
to rot after a hunt. They are now almost extinct. 




Evolution of the horse. The illustration is a scientist's sketch of the earliest 
horse, which became extinct many ages ago. It was about the size of a fox; the 
bones of its head and fore foot are shown at the left. The bones of the present 
horse's head and fore foot are shown at the right. Between are those of animals 
intermediate in the line of descent. 

Geologic History of the Horse. — In some ungulates the 
middle toe of the foot has become largely developed, with the 
result that the animal stands on it. Among such animals are 
the zebra and the horse. 



308 THE VERTEBRATE ANIMALS 

We have, from time to time, made reference to the fact that 
certain forms of Hfe, now ahnost extinct, flourished on the earth 
in former geologic periods. It is interesting to note that America 
was the original home of the horse, although at the time of the 
earHest explorers the horse was unknown here. The wild horse of 
the Western plains descended from horses introduced by the 
Spaniards. Long ages ago, the remote ancestors of the horse were 
probably little animals the size of a fox, with five-toed feet. 
The earliest horse we have knowledge of had faur toes on the fore 
and three toes on the hind feet. Thousands of years later there 
existed a larger horse, the size of a sheep, with three toes on each 
foot. By gradual changes, caused by the tendency of animals 
to vary, there was eventually produced our present horse, 
an animal with legs adapted for rapid locomotion, with 
feet particularly fitted for life in open fields, and with teeth 
which serve well to seize and grind herbage. 

Domestication of Animals; Breeding by Selection. — The 
prehistoric horse for some reason disappeared in this country, 
but continued to exist in Europe, and man, emerging from his 
early savage condition, began to make use of the animal. We 
know the horse was domesticated in early Biblical times, and 
that it became one of man's most valued servants. In more 
recent times, superior horses have been developed by selective 
breeding. 

To do this, the horses that have varied and show the char- 
acteristics desired by the breeder are selected and bred together. 
The young from these animals are likely to be like their par- 
ents and may be even more likely to show the characteristics 
the breeder desires. If this process is repeated for several 
generations, it will be seen that man, by artificial selection, 
may have considerably modified the type of horse with which 
he started. In this manner the various types of horses familiar 
to us as draft horses, coaches and hackneys, and the trotters 
have been established and improved. In a similar manner the 
various breeds of cattle, sheep, swine, and other domestic 
animals have been obtained. 

It is needless to say that man has caused a tremendous 
change in animals by domesticating them and by selective 



MAMMALS 



309 




breeding. When we realize the very great amount of money 
invested in domesticated animals; and that there are over 
50,000,000 each of sheep, cattle, and swine and over 20,000,000 
horses owned in this country, we may see how important a 
part domestic animals play in our lives. 

Orders of Mammals. — The lowest are the monotr ernes, animals which 
lay eggs hke the birds, although they are provided with hairy covering 
Uke other mammals. Such are the AustraUan spiny anteater and the 
duck mole. 

All other mammals give birth 
to young which are developed to 
a form similar to their own. 
The kangaroos and opossums, 
however, are provided with a 
pouch on the ventral side of the 
body in which the very im- 
mature, blind, and helpless young 
are nourished until they are able 
to care for themselves. These 
pouched animals are called 
marsu'pials. 

The other mammals, in which 
the young are born able to care for themselves, and have the form of 
the adult, may briefly be classified as follows: 

Order I. Edenta'ta. Toothless or with very simple teeth. Examples: 
anteater, sloth, armadillo. 

Order II. Ceta'cea. Adapted to marine life; teeth (of whales) sometimes 
platelike. Examples: whale, porpoise. 

Order III. Sire'nia. Fishlike; pectoral limbs paddle-like; pelvis absent, 
no vertical dorsal fin. Examples: manatee, dugong. 

Order IV. Roden'tia. Incisor teeth chisel-shaped, usually two above and 
two below. Examples: beaver, rat, porcupine, rabbit, squirrel. 

Order V. Ungula'ta. Hoofs; teeth adapted for grinding. Examples: (a) 
odd-toed: horse, rhinoceros, tapir; (6) even-toed: ox, pig, sheep, 
deer. 

Order VI. Insectiv'ora. Small, insect-eating, furry or spiny covered; 
long snout. Examples: mole, shrew, hedgehog. 

Order VII. Carniv'ora. Long canine teeth, sharp and long claws. Exam- 
ples : dog, cat, bear, seal, and sea Hon. 

Order VIII. Chiroptera (ki-rop'te-ra) . Fore Hmbs adapted to flight, 
teeth pointed. Example: bat. 

Order IX. Primates (pri-ma'tez). Erect or nearly so, fore appendage pro- 
vided with hand. Examples: monkey, ape, man. 



Virginia opossum. Photograph, one eighth 
natural size, by N. F. Davis. 



310 THE VERTEBfL^TE AXIMALS 

Summary. — The mammals are vertebrates with hair, warm 
blood, fom'-chambered heart, and mammary glands. Economi- 
cally they are of much importance as they fm-nish us with food, 
beasts of bm-den, clothing, etc. Some are of distinct haiTQ, the 
rat being perhaps the gi*eatest offender. 

Problem Questions. — 1. Why are mammals considered the 
highest animals? 

2. How would you distinguish a rodent? A carnivorous 
mammal? An ungulate? 

3. Name the local mammals found in vom' com m unit v that 
are of value; of harm. 

Problem and Peoject Refzrexces 

Hodge, Xature Study and Life, Chapter III. Ginn and Company. 

Ingersoll, Wild Xeighbors. The ]Macmillan Company. 

Matthew, The Ecolution of the Horse. Guide Leaflet Xo. 9. American Museurc 

of Natural History. 
Stone and Cram, American Animals. Doubleday, Page, and Company. 
Wright, Four-footed Americans. The Macmillan Company-. 



XXIII. MAN, A MAMMAL 

Problem, To compare man as a vertebrate with the frog as to — 
(a) Body covering, 
(6) Muscles. 

(c) Adaptations in the skeleton. 

(d) Nervous system. 

(Laboratory Manual, Prob. XLI; Laboratory Problems, Probs. 
163 to 169.) 

Man's Place in Nature. — -Although we know that man is 
separated mentally by a wide gap from all other animals, in om- 
study of physiology we must ask where we are to place him 
structurally. If we attempt to classify man, we see at once he 
must be placed with the vertebrate animals because of his pos- 
session of a vertebral column. Evidently, too, he is a mam- 
mal, because the young are nourished by milk secreted by the 
mother and because his body has at least a partial covering of 
hair. Among the different orders of manmials man most closely 
resembles anatomically the one to which the monkeys and apes 
belong, called primates. 

Although anatomically there is a greater difference between 
the lowest type of monkey and the highest type of ape than 
there is between the highest type of ape and the lowest savage, 
yet there is an immense mental gap between the ape and man. 

Evolution of Man. — Undoubtedly there once lived upon the 
earth races of men who were much lower in their mental organi- 
zation than the present inhabitants. If we follow the early 
history of man upon the earth, we find that at first he must have 
been little better than one of the lower animals. He was a 
nomad, wandering from place to place, living upon whatever 
animals he could kill with his hands and whatever edible plants 
he found. Gradually he learned to use weapons, with which to 
kill his prey, first using rough stone implements for this purpose. 

311 



312 MAN, A MAMMAL 

As man became more civilized, implements of bronze and of 
iron were used. About this time the subjugation and domesti- 
cation of animals began to take place. Man then began to 
cultivate the fields, and to have a fixed place of abode other than 
a cave. The beginnings of civilization were long ago, but even 
to-day the earth is not entirely civilized. 

The Races af Man. — At the present time there exist upon 
the earth five races or varieties of man, each very different 
from the others in instincts, social customs, and, to an extent, in 
structure. These are the Ethiopian or negro type, originating 
in Africa; the Malay or brown race, from the islands of the 
Pacific; the American Indian; the Mongohan or yellow race, 
including the natives of China and Japan, and the Eskimos; 
and, finally, the Caucasians, represented by the civilized white 
inhabitants of Europe and America. 

The Human Body a Machine. — In all animals, and the 
human animal is no exception, the body has been Hkened to a 
machine in that it turns over the latent or potential energy 
stored up in food into kinetic energy (mechanical work and 
heat), which is manifested when work is performed. One great 
difference exists between an engine and the human body. The 
engine uses fuel unlike the substance out of which it is made. 
The human body, on the other hand, uses for fuel the same 
substances as those out of which it is formed; it may, indeed, 
use part of its own substance for food. The human organism 
must do more than purely mechanical work; it must be so 
delicately adjusted to its surroundings that it will react in a 
ready manner to stimuli from without; it must be able to 
utilize its fuel (food) in the most economical manner; it must 
be fitted with machinery for transforming the energy received 
from food into various kinds of work; it must properly provide 
the machine with oxygen so that the fuel will be oxidized, and 
it must carry away the products of oxidation, as well as other 
waste materials which might harm the effectiveness of the 
machine. Most important of all, the human machine must 
be able to repair itself. 

In order to understand better this complicated machine, the 
human body, let us examine the structure of its parts and thus 



THE HUMAN BODY 



313 



get a better idea of the interrelation of these parts and of their 
functions. 

Structure of the Skin. — In man, the outer covering, or skin, 
is composed of two layers: the epidermis and the dermis. The 
outer part of the epidermis is made largely of flattened dead 
cells. It is this layer that peels off after sunburn, or that sep- 
arates from the inner part of the epidermis when a water blister 
is formed. The inner cells of the epidermis are provided with 
more or less pigment or coloring matter. It is to the varying 



Sweat-Ihui 



Bomy layer 
Pigment layer 

Xaetile Organs' 
Nerve — 
Stood Teasels --^ 

Svoeat Gland 
Fat 




EpidermU 



>Demia 



Subcutarteous layer of ^ 
'connective tissue arid jOt 



Diagram of a section of the skin. (Highly magnified.) 

quantity of this pigment that the light or dark complexion is 
due. The inmost part of the epidermis is made up of small 
cells which are constantly dividing to form new cells to take 
the place of those in the outer layer which are lost. 

The dermis, or inner layer of the skin, is largely composed of 
connective tissue filled with a network of blood vessels and 
nerves. This layer contains the sweat glands, some of the most 
important glands in the body, and the tactile cor'puscles, which 
^re connected with the nervous system, and cause this part of 
the skin to be sensitive to touch. 

Nails and Hair. — Nails are a development from the horny 
layer of the epidermis. A hair is also an outgrowth of the horny 

HUNT. XBW ES. 21 



314 



MAN, A MAMMAL 



layer, although it is formed in a deep pit or depression in the 
dermis; this pit is called the hair follicle. 

The Glands of the Skin. — Scattered through the dermis, and 
usually connected with the hair follicles, are tiny oil-secreting 
glands, the sebaceous (se-ba'shus) glands, which keep the hair 
and surface of the skin soft. The other glands in the dermis, 
known as sweat glands, are to be found in profusion, over 
2,500,000 being present in the skin of a normal man. These 
glands excrete certain wastes from the blood in the water they 
pass off. Thus the skin not only protects the body, but also 
serves as an excretory organ. Its most important function, how- 
ever, is the regulation of the heat of the body. How it does 
this, we shall learn later. (See Chapter XXVII.) 

Connective Tissue. — The layer immediately beneath the der- 
mis is known as the suhcuta'neous layer. It is an important 
storage place for fat. Underneath this layer we find a mass 

of flesh or muscle. Intermixed with this is 
a considerable amount of fat. The fat, 
muscle, — in fact, all the tissues in the 
body, — are held together by fibrous threads 
called connective tissue. 

Muscles and Movement. — We are all 
aware that motion in any of the higher 
animals is caused by the action of the 
muscles, which contract to cause movement. 
In man and the other vertebrate animals, 
the muscles are almost always fastened to 
bones, which, acting as levers, give wide 
range of motion. 

Arrangement of Voluntary Muscles in 
the Human Body. — Muscles are usually 
placed in pairs; one, called the extensor y 
muscle; sm, a flexor serves to straighten the joint; the other, 
^^^^ ^' the flexor, bends the joint. Locate, by feel- 

ing the muscles when expanded and when contracted, the 
extensors and flexors in your own arm. This paired arrange- 
ment of muscles is of obvious importance, a flexor muscle 
balancing the action of an extensor on the other side of the 




sm 



Frog's hind leg: tr, 
triceps, an extensor 



THE HUMAN BODY 



313 




joint. The end of the muscle that 
has the wider movement in a 
contraction is called the inser- 
tion; the part that moves least 
is the origin. 

Microscopic Structtire of Volun- 
tary Muscle. — With a sharp pair of 
scissors cut through a muscle at right 
angles to the long axis; examina- 
tion will show that it is composed of 
a number of bundles of fibers. These 
fibers are held together by a sheath 
of connective tissue. Each of these 
bundles may be separated into 
smaller ones. If we continue this so 
as to separate the smallest possible 
bits that can be seen with the naked 
eye, and then examine such a tiny 
portion under the compound micro- 
scope, it will present somewhat the 
appearance shown in the Figure. The 
muscle is seen to be made up of a 
number of tiny threads which lie side 
by side, held together by the sheath. 
Muscles, then, are bundles of long 
fibers. In man, muscles which are under the control of the will have a 
striated appearance, while those which are involuntary are unstriated. 
Both kinds are supplied with nerves, which control them (see Figures). 

Muscle Tissue and its Uses.' 
— Muscles form a large part of 
the body, in man nearly half 
of his entire weight. Nearly 
every muscle in the human body 
is attached to a bone either at 
one or at both ends. Move- 
ment is performed by means of 
the muscles, leverage being ob- 
tained by their attachment to 
the bones. In the human body 
^, , ,. , ,. ^ . , there are over five hundred mus- 

1 he delicate endings of nerves m vol- . „ 

untary muscle. (Highly magnified.) . .cles, varying from one Smaller 



A bit of voluntary muscle fiber, 
showing the cross striations as seen 
under the microscope. (Highly mag- 
nified.) 




316 



MAN, A MAMMAL 



than a pinhead to a band almost two feet in length. Every 
movement of the body, be it merely a change of expression or 
change in the pitch of the voice, directly results from contrac- 
tion of a muscle. Muscles also give form to the body, and are 
useful in protecting the delicate organs and large blood vessels 
within them. 

Muscles and the Skeleton. — Muscles would be of little use 
to animals if they were not attached to hard parts of the body 
which serve as levers. In many invertebrate animals (for ex- 
ample, crustaceans, insects, and mollusks), the muscles are 
attached to the exoskeleton. In man they are attached to the 
endoskeleton. 

In the hind leg of a frog, if we cut through the muscles of the thigh 
to the bone, we may make out exactly how and where the muscles of 
the thigh are attached to the bone. Moving the leg in as many different 
directions as possible, we notice that it may be flexed or bent; that it 
may be extended to its original position; that it may be moved to and 
from the midline of the body; that, with the knee held stiff, the whole 
limb may be made to describe the arc of a circle.^ 

The same movements are possible in the leg of a man. This move- 
ment between bones is obtained by means of joints. If, in the frog, we 
carefully separate the muscles of the thigh to the bone, 
we find that they are attached to the bone by white, 
glistening tendons. Careful examination shows that the 
bones themselves are held together by very tough white 
bands or cords; these are the ligaments. We find, too, 
that one end of the large thigh bone fits into a socket 
in the hip bone or pelvic arch. It is thus easy to see 
how such free movement is obtained in the leg. 

Levers in the Body. — It is evident that movement 
of a joint is caused by muscles which act in cooperation 
with the bones to which they are attached; the latter 
thus form true levers. A lever is a structure by Vhich 
either greater work -power or greater range of motion is 
obtained. In this apparatus, the lever works against a 
fixed point, the fulcrum, in order to raise a certain 
weight. A seesaw is a lever; here the fulcrum is in 
the middle, the weight is at one end, and the power to 
lift the weight is applied at the other end. There are three classes of 
levers, named according to the position of the fulcrum. 

1 At this point, if possible, demonstration with a human skeleton should be 
made. 




Hinge joint, 
showing muscle 
(a) and its ten- 
don (6). 



THE HUMAN BODY 



317 



In the first class, the fulcrum lies between the weight and the force or 
power; the seesaw is an example of this. The best example in the human 
body of a lever of the first class is seen when the head is raised. Here the 
fulcrum is the vertebra known as the atlas; the power is the muscles of 
the neck attached to the back of the skull and to the spine; the weight is 



Levers of the first Class 



ful 



crum 



force 



weight 




F W 




"^^ 



Levers of the second Class 
fulcrum 



weight 



F W 



force 





Levers of the third Class 

fulcrum 



weight 



force 




P^ 



Three classes of levers: the first case shows pushing with the toe; the second, rising 
on the toe; the third, lifting with the toe. 

the front part of the head. When one keeps the head erect, this lever is 
used; the nodding head when one is napping shows its action. 

A lever of the second class has the fulcrum at one end, and the weight 
between it and the pqwer; when we rise on our toes, we use this kind of 
lever. 

In a lever of the third class, the fulcrum is at one end, with the power 
between it and the weight. This is the kind of lever seen most frequently 
in the human body. The flexing (drawing up) of the lower leg or the fore- 
arm is an example of the use of this kind of lever. In such a lever, a wide 
range of movement is obtained. 

General Structure and Uses of the Skeleton. — Evidently 
bones form a framework to which muscles are attached; thus 
they are used as levers for purposes of movement. Second, 
they give protection to delicate organs; they form a case around 



31S 



MAN, A MAMMAL 




the brain and spinal cord; as ribs they protect the organs in 

the body cavity. Third, they give rigidity and form to the 

body. 

The skeleton of vertebrate animals consists of two distinct 

regions: a ver'tehral column or backbone which, with the skull, 

forms the axial skeleton; 
and the parts attached to 
this main axis, the appen- 
dic'ular skeleton (the ap- 
pendages). All skeletons 
of vertebrates have the 
same general regions, the 
size and shape of the bones 
in these regions differing 
somewhat in each kind of 
% animal. 

Skeleton of a dog, a typical mammal. ' In the axial skeleton the 

vertebral column is made up of a number of bones of irregular 
shape, which fit more or less closely into each other. This 
can be seen easily in the frog. These bones are called vertehroe. 
They possess long processes to some of which the muscles of the 
back are attached. Certain of the vertebrae bear ribs (arched, 
flat bones), the special function of which is to protect the organs 
of the upper body cavity. 

Adaptations in the Vertebral Column. — The vertebral column 
in a child is made of thirty-three separate pieces of bone; sev- 
eral of them grow together in 
the region of the pelvis and 
there are twenty-six in the 
adult. Each vertebra presents 
the general form of a body or 
centrum of bone and a bony 
arch with seven projections; 
in this arch runs the spinal 
cord. The vertebra directly 
beneath the head is modified so as to permit the skull to rest 
in it; this articulates freely with the second vertebra, thus 
permitting the nodding and turning movements of the head. 




Vertebra, showing attachment of ribs: 
C, centnmi; R, ribs;<SP, spinous process. 



THE HUMAN BODY 



319 



Besides these individual adaptations, the vertebral column, as a 

whole, is peculiarly adapted to protect the brain from jar; this 

is seen in the double bend of 

the vertebral colimm and the 

pads of cartilage between the 

individual vertebrae. The 

whole column of vertebrae 

joined one above another 

supports the weight of the 

body. The largest vertebrae 

at the base of the column 

are joined to the huge pelvic 

bones to support the body 

above. That part of the 

vertebral column of man 

which bears the ribs is known 

as the thoracic (th6-ras'ik) 

region. The ribs, twelve pairs 

in number, are long, curved 

bones which combine lightness 

with strength; joined by 

elastic cartilage to the ster' 

num in front and to the 

vertebrae behind, they form a 

wonderful protection to the 

organs in the thoracic cavity, 

and yet allow free movement 

in breathing. 

The Appendages. — The 
parts of the skeleton to which 
the bones of the anterior and 
posterior appendages are 
attached are respectively 
known as the pectoral girdle 
(from which hangs the arm) 




Skeleton of man: CR, cranium; CL, 
clavicle; ST, sternum; H, humerus; VC, 
vertebral column; P, pelvic girdle; i2, 
radius; U, ulna; C, carpals; M, meta- 
carpals; Ph, phalanges; F, femur; T, tibia; 
Fi,Ghvla.; Tar, tarsals; MT, metatarsals. 



and the pelvic girdle (which joins the leg bones to the axial 
skeleton). 
The bones of the appendages attached to the pelvic girdle 



320 



MAN, A MAMMAL 



are adapted peculiarly to locomotion and support; for this 
purpose the bones are long and strong, hinged by very flexi- 
ble joints. In the hand the joints are especially free to 
allow for grasping. In the leg, where weight must be sup- 
ported as well as carried, the bones are bound more firmly 

to the axial skeleton. 
The bones of the foot 
are so arranged that a 
springy arch is formed 
which aids greatly in 
locomotion. 

The Human Skull. — The 

skull shows wonderful adap- 
tations for protection; it is 
compactly built, and its 
arched roof gives strength. 
The eye and inner ear are 
protected in sockets of bone. 
The lower jaw works upon a 
hinge, and furnishes attach- 
ment for strong muscles which 
move the jaw. 




• The skull: F., frontal bone; P., parietal 
bone; T., temporal bone; SP., sphenoid bone; 
O., occipital bone; U.J., superior maxillary 
(upper jaw) bone; L.J.^ inferior maxillary 
(lower jaw) bone. 



Other Organs. — We have seen that a body cavity has de- 
veloped in all animals which are more complex than the bag- 
like hydra, and that a food tube has come to lie within this 
space. In all such animals the structures which have to do 
with digestion and absorption of food, most of those which have 
to do with the circulation of food and of the blood, and organs 
which give oxygen to the blood, as well as the organs of excre- 
tion and of reproduction, lie within the body cavity. These 
organs we shall discuss in detail later. 

Nerves. — Nerves are found in practically all parts of 'the 
body, ending in the skin, in muscle, in the heart, lungs, and other 
organs, where they receive stimuli and control movements. 
The most important part of the nervous system in vertebrate 
animals lies within the cavity formed by bones making up 
the skull and the vertebral column. This central nervous 
system, consisting of the spinal column and the hrain, is a 
characteristic of the vertebrates. 



THE HUMAN BODY 321 

General Functions of the Nervous System. — We have seen 
that, in the simplest animals, one cell performs the functions 
necessary to its existence. In the more complex animals, where 
groups of cells form tissues, each having a different function, 
a nervous system is developed. The functions of the human 
nervous system are: (1) to ^provide man with sensation, by means 
of which he becomes acquainted with the world about him; (2) to 
connect organs in different parts of the body so that they act as a 
united and harmonious whole; (3) to provide for the acts which 
we call voluntary. Cooperation in word and deed is the end 
attained. We are all familiar with examples of the cooperation 
of organs. You see food; the thought comes that it is good to 
eat; you reach out, take it, raise it to your mouth; the jaws 
move in response to your will; the food is chewed and swal- 
lowed; while digestion and absorption of the food are taking 
place, the nervous system is still in control. The nervous 
system regulates the pumping of blood to all parts of the body, 
respiration, secretion of glands, and, indeed, every bodily func- 
tion. Man is the highest of all animals because of the extreme 
development of the nervous system. Man is the thinking 
animal, and as such is master of the earth. 

Summary. — Man is a mammal. He is also anatomically a 
complicated machine. This chapter has pointed out numerous 
adaptations in the skeleton and muscles of the body. It has 
also pointed out that coordination is brought about by means of 
the nervous system. • 

Problem Questions. — 1. Why is man a mammal? 

2. Mention ten adaptations in the human skeleton. 

3. How is movement brought about in the body? 

4. What are the functions of the different parts of the nervous 
system of man? 

Problem ajstd Project References 

Burton-Opitz, Physiology. W. B. Saunders Company. 

Clodd, Primer of Evolution. Longmans, Green, and Company. 

Eddy, General Physiology. American Book Company. 

Hough and Sedgwick, The Human Mechanism. The Macmillan Company. 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Ritchie, Human Physiology. World Book Company. 

Sharpe, A Laboratory Manual. American Book Company. 



XXIV. FOODS AND DIETARIES 



Problem. A study of food values and diets to determine — 

SULPHUR ao3lU^oo% ^^^ ^^^^ ^^^^^^ ^^^ ^^^^' 



'PHQSPH0RU51 
CALCIUM 



nttrogenP^ 



NfTROGEH 
3.13X65. 



HYDROGEN 
I3.65\bs. 



,.2iG\ts. )}% I ' (b) Nutritive values as compared with 
o.z7?Th»X% cost. 

(c) The family dietary, 

(d) Food values. 
(Laboratory Manual, Prob. XLII; 

Laboratory Problems, Probs, 170 to 178.) 



CARBON, 



OXYGEN 

^- i08.l5lb;5. ' 



^ 



Why we need Food. — We have 
already defined food as anything that 
forms material for the growth or repair 
of the body of a plant or animal, or that 
furnishes energy for it. The milHons 
of cells of which the body is composed 
must be given material which will 
form more living matter or material 
which can be oxidized to release en- 
ergy when muscle cells move, or gland 
cells secrete, or brain cells think. 
Food, then, not only furnishes our body 
with material to grow, but also gives 
us the energy we expend in the acts 
of walking, running, breathing, and 
even in thinking. 
Nutrients. — Certain nutrient materials form the basis of food 
for both plants and animals. The organic nutrients have been 
found to be proteins (such as lean meat, eggs, the gluten of 
bread), carbohydrates (starches, sugars, gums, etc.), fats and oils 
(both animal and vegetable), and vitamins. The inorganic 
nutrients are mineral matter and water. The parts of the human 
body, be they muscle, blood, nerve, bone, or gristle, are built 
up from the nutrients in our food. 

322 



The chief chemical elements 
of which the human body is 
composed, with percentage of 
each. The weight also is 
given, for a body weighing 
150 pounds. 



NUTRIENTS 323 

Proteins. — Proteins, in some manner unknown to us, are 
manufactured in the bodies of green plants. They contain the 
element nitrogen, and hence are called nitrogenous foods. 
Nitrogen, necessary for the growth of the body, can be used 
only when combined with other elements in the form of a com- 
pound. Man forms the protoplasm of his body (that is, the 
muscles, tendons, nervous system, blood corpuscles, the living 
parts of the bone and the skin, etc.) from nitrogenous food. 
Different proteins contain different amounts of available build- 
ing material, hence some are more useful to the body than 
others. Proteins may also be used as fuel in the body. Some 
nitrogenous food man obtains by eating the flesh of animals, and 
some he obtains directly from plants (for example, peas and beans). 

Fats and Oils. — Fats and oils, both animal and vegetable, 
are the materials from which the body derives part of its 
energy. The chemical formula of a fat shows that while it has 
considerable carbon and hydrogen in its molecule, there is very 
httle oxygen present; hence the great capacity of this sub- 
stance for uniting with oxygen. A pound of butter releases 
over twice as much energy to the body as does a pound of 
sugar or a pound of steak. Human fatty tissue is formed in 
part from fat in the food eaten, but carbohydrate or even protein 
food may be changed into fat and may be stored in the body as 
a reserve supply of fuel. 

Carbohydrates. — The carbohydrates, like the fats, contain 
carbon, hydrogen, and oxygen. Here, however, the oxygen 
and hydrogen are united in the molecule in the same pro- 
portion as are hydrogen and oxygen in water. Carbohydrates 
are essentially energy-producing foods. 

Vitamins. — Vitamins are not very well known but they have 
been proved to be necessary for Hfe. They may be destroyed 
easily by heat in some foods, as milk, and endure a great deal 
of heat in others, as potatoes and tomatoes. Four or more vita- 
mins have been identified : A, found in milk, butter, eggs, and 
some vegetables, as spinach, carrots, and sweet potatoes ; B, 
found in the outer layers of cereals, in most vegetables and fruits, 
yeast, and milk ; C, found in some fruits and vegetables ; and D, 
found in milk and certain green vegetables. The action of the 



324 



FOOD AND DIETARIES 



^ 
5 






^ 







/8'^DAY^ 


/H 


^/ /8"'DAY 


f 



Days 



The importance of vitamins. Two 
groups of rats were fed ample rations 
of protein, carbohydrate, fat, and mineral 
salts, similar to those in milk. In addi- 
tion a minute quantity of milk, contain- 
ing the vitamin missing from the regular 
rations, was given to group A only for 
the first seventeen days, and to group 
B only thereafter. What was the effect 
upon growth, as shown by the average 
weight? 



fluids, and a sufficient 



third vitamin, C, is partly 
destroyed hy heat, so preserv- 
ing and canning foods render 
such foods less valuable as 
givers of vitamins. 

Just what service the vita- 
mins do is unknown, but we 
do know" that if om' diet does 
not contain all of them, growth 
will not take place and illness 
or even death may follow. 
Scm-vy, beriberi, and probably 
rickets are due to the absence 
of certain \dtamins. 

Inorganic Foods. — Water 
forms a large part of almost 
every food substance. The 
human body, by weight, is 
about 65 per cent water. 
Water forms a large part of 
the blood and the digestive 
quantity is essential to health. 




Foods rich in ^atamins : "A" is contained in milk, butter, and eggs; "B," in 
vegetables, oranges, whole- wheat bread, and milk ; " C," in oranges and fresh vege- 
tables ; and " D," in milk and green vegetables. 

When we drink water, we take with it some of the inorganic 
salts used by the body in making bone and in the formation 



NUTRIENTS 



825 



BREAD, (WATER) 
" , (MILK) 

" , wHQu wHEiT mm 
" , " " otm- 

BARLEY (WHOLE) 

CORN, YELLOW 

OATS 

RYE, CRACKED 

WHEAT, KERNEL 
" , BRAN 

LIVER 

KIDNEY 

BRAINS 

HEART 

FISH, FAT 

•' , ROE 

MILK, FRESH, (UIIFUTEIIRIZED) 
" , CONDENSED 
" , EVAPORATED 

" , DRIED, mm- ■ 

" , SKIMMED •■ 

BUTTERMILK 

CREAM 

BUTTER 

CHEESE 

EGGS • 

ALMONDS 

COCONUT 

HICKORY NUTS 

PEANUTS 

WALNUTS 



"A" 



+ 

+ 
++ 

■I- 

+ 

+ 

+ 
++ 

+ 
++ 
++ 

+ 

+ 

+ 

4 
+++ 
+++ 
+++ 
+++ 

+ 

+ 
+*+ 
+++ 
++ 
+++ 

+ 

+ 

+ 
* 



+ 

++ 
++ 
++ 
++ 
++ 
++ 
+++ 
+++ 
+ + 
++ 
++ 

+ 

■♦■ 

++ 
++ 
++ 
++ 
++ 

+ 
++ 
++ 

++ 
+ 
++? 
++ 
++ 
++ 
+4- 



"C" 



+ 

+ 
9 

++V 

+v 
? 

+v 
+v 

4V 
+V 



+ 
+ 
+ 
+ 

+ 
++ 

+ 



TOMATO m 08 mm ■ • 

BEANS, KIDNEY 

" , NAVY 

" , STRING 

BEETS 

CABBAGE, RAW 

, CANNED 
" , COOKED bhiefu 
CARROT, RAW 

" , COOKED 
CAULIFLOWER 
DANDELION GREENS 
LETTUCE (GARDEN) 
ONIONS 

PARSNIP 

PEAS, FRESH 

POTATO (BOILED) 

SWEET POTATO 

RUTABAGA 

SPINACH, FRESH 

CANNED • 

SQUASH 

TURNIPS 

APPLES 

BANANAS 

GRAPE JUICE 

GRAPEFRUIT 

LEMON JUICE 

ORANGE JUICE 
PINEAPPLE (UW Ofl CtNNED) 
RASPBERRIES (UW OR CtNNEtl) 
F'EACHES m OR CANKED) - 



'A" 



++ 

+ 
+ 
++ 

++ 

* 

++ 
++ 
++ 

+ 

++ 
++ 

? 

++ 

•f 
++ 

+++ 
+++ 
++ 

+ 
? 

7 

+ 
++ 

++ 



'B- 



+++ 

+++ 

+++ 

++ 

+ 

* 
++ 

+ 

+ 

++ 
++ 
++ 
++ 
++ 
++ 
++ 

+ 
++ 
+++ 

+ 

? 
++ 
++ 

+ 

+ 
+♦ 
++ 
+♦ 
++ 

* 

+ 



"C" 



+++ 

* 

+ 

+ 
■f+4- 
++ 

+ 

+ 
+V 

7 

+ 
+++ 
++ 

7 
+++ 
++ 

7 
+++ 
+++ 

4-i-i- 

7 

*** 

++ 

+ 

+ 

++ 

+++ 

+++ 

+++ 

+++ 

++ 



■contains the Vitamin 
good source of the Vitamin 
excellent source of the Vitamin 
mm. ■ -no appreciable amount of the Vitamin 



?• • doubt as to presence or relative 
amount 

*■ ■ evidence lacking or insufficient 
V- • variable 



Vitamins in foods. From the American Medical Association. 



of protoplasm. Sodium chloride (table salt), an important part 
of the blood, is taken as a flavoring upon our meats and vege- 
tables. Phosphate of lime and potash are important factors in 
the formation of bone. 

Phosphorus is a necessary element for making protoplasm. 
Milk, eggs, meat, whole wheat, and dried peas and beans con- 
tain small amounts of it. Iron also is an extremely impor- 
tant mineral, as it is used in the building of red blood cells. 
Meats, eggs, peas, beans, spinach, and prunes are foods contain- 
ing some iron. 



326 FOOD AND DIETARIES 

Some salts, compounds of calcium, magnesium, potassium, 
and phosphorus, have been recently found to aid the body 
in many of its most important functions. The beating of the 
heart, the contraction of muscles, and action of the nerves 
appear to be due to the presence of minute quantities of these 
salts in the body. 

Uses of Nutrients. — The following table sums up the uses 
of nutrients to man: 



All serve as fud 

and yield energy in 

► form of heat and 

muscular strength. 



Protein Forms tissue (muscles, 

White (albumen) of eggs, curd tendon, and prob- 
(casein) of milk, lean meat, ably fat), 
gluten of wheat, etc. 

Fats Form fatty tissue. 

Fat of meat, butter, olive oil, 
oils of corn and wheat, etc. 

Carbohydrates Transformed into fat. 

Sugar, starch, etc. 

Vitamins • • • • Accessory substances of unknown com- 
position that seem to be regulating and 
growth promotiug. They are essential 
to life. 

Mineral matters (ash) .... Aid in forming bone. 
Phosphates of lime, potash, assist in digestion, etc. 
soda, etc. 

Fuel Values of Nutrients. — In planning for the diet best 
fitted for our daily requirements the food used for energy in 
the body is stated in heat units called caVories. A calorie 
(large calorie) is the amount of heat required to raise the temperature 
of one kilogram of water one degree Centigrade. This is about 
equivalent to raising one pound of water four degrees Fahrenheit. 
The fuel value of different foods may be computed accurately by 
burning a given portion (say one pound) in the apparatus known 
as a calorim'eter. 

The Best Diet. — Inasmuch as all 'living substance contains 
nitrogen, it is evident that protein food must form a part of 
the dietary; but protein alone will not support life. If more 
protein is eaten than the body requires, immediately the liver 
and kidneys have to work overtime to get rid of the excess of 
protein which forms poisonous wastes. 



THE BEST DIET 327 

It has been found that a man who does muscular work requires 
a Uttle less than one quarter of a pound of protein, the same 
amount of fat, and about one pound of carbohydrate to provide 
for the growth, waste, and repair of the body and the energy 
used up in one day. Put in another way, Atwater's standard 
for a man at light exercise is food enough to yield 2816 calories; 
of these, 410 calories are from protein, 930 calories from fat, 
and 1476 calories from carbohydrate. That is, for every 100 
calories furnished by the food, 14 are from protein, 32 from 
fat, and 54 from carbohydrate. In actual amount, the day's 
ration as advocated by Atwater would contain about 100 grams 
or 3.7 ounces protein, 100 grams or 3.7 ounces fat, and 360 grams 
or 13 ounces carbohydrate. Professor Chittenden of Yale Univer- 
sity, another food expert, thinks we need proteins, fats, and carbo- 
hydrates in about the proportion of 1 to 3 to 6, thus differing 
from Atwater in giving less protein in proportion. Chittenden's 
standard for the same man is food to yield a total of 2360 
calories, of which protein furnishes 236 calories, fat 708 calo- 
ries, and carbohydrates 1416 calories. For every 100 calories fur- 
nished by the food, 10 are from protein, 30 from fat, 60 from 
carbohydrate. In actual amount the Chittenden diet would 
contain 2.16 ounces protein, 2.83 ounces fat, and 13 ounces 
carbohydrate.^ A German named Voit gives as ideal 25 proteins, 
20 fat, 55 carbohydrate, out of every 100 calories; this is nearer 
our actual daily ration. In addition, an ounce of salt and 
nearly one hundred ounces of water containing the necessary 
mineral salts, are used in a day. 

In addition to this the diet must include foods containing 
vitamins. By means of the table on the following page (from 
Atwater ^), which shows the composition of some food mate- 
rials, the nutritive and fuel value of the foods may be seen 
at a glance. The amount of refuse contained in foods (such 
as the bones of meat or fish, the exoskeleton of crustaceans 
and moUusks, the woody coverings of plant cells) is also 
shown in this table. 

iPage 18, Bui. 6, Cornell Reading Course. 

2 W. O. Atwater, Principles of Nutrition and Nutritive Value of Food, U.S. 
Department of Agriculture. 



328 



FOOO AND DIETARIES 



DIGESTIBLE NUTRIENTR 



INDIGESTIBLE 
NUTRIENTS 



MUSCLE 
MAKING 



FATS CARBO- MINERAL 
HYDRATE^ MATTERS 



NON NU TRIENTS 
WATER RKFtTRE 



-~ FUEL VALUF 
CALORIES 



FUEL INGREDIENTS 



NUTRIENTS. ETC. 
PER CENT. 



10 



20 



30 



40 



50 



60 



70 



80 



90 



\oo 



FUEL VALUE OF 
1 LB. (calories) , 



400 800 1,200 2.000 2,200 2,400 2,800 3,200 3,600 4,000 




'M Ife 



B^ 



Milk, 
■nnskiiruned 

Butter 



.mm&.M^;^ ;r. r Ife.-^-^" 



White bread 



IWgW 



Oat meal 




Com meal 



Rice 



^^ 



Beans 



t 



Potatoes 



Sugar 



Table of food values. Determine the percentage of water in codfish, loin of 
beef, milk, potatoes. Percentage of refuse in leg of mutton, codfish, eggs, and 
potatoes. What is the refuse in each case? Find three foods containing a high 
percentage of protein; of fat; of carbohydrate. Find some food in which the 
proportions of protein, fat, and carbohydrate are combined in the right proportions. 



THE BEST DIET 



829 




Vat 
sugar 
%^protein 
minerals 



water 



A Mixed Diet Best. — Knowing the proportion of the different 
food substances required by a man and the ones containing the 
vitamins, it will be an easy matter to determine from this 
table the best foods for use in a mixed diet. Meats contain 
so much nitrogen that they should be eaten with other foods. In 
milk, the proportion of proteins, carbohydrates, and fats is 
nearly right to make protoplasm; a consider- 
able amount of mineral matter and at least 
two of the vitamins being also present. For 
these reasons, milk is extensively used as a 
food for children. Why? Some vegetables 
(for example, peas and beans) contain the 
nitrogenous material needed for protoplasm 
formation in considerable proportions, but in 
a less digestible form than is found in some 
other foods. A purely vegetable diet contains 
much waste material, such as the cellulose 
forming the walls of the plant cells, which is 
indigestible. The Japanese army ration used 
to consist almost entirely of rice. A recent 
report by their surgeon-general intimates that the diminutive 
stature of the Japanese may, in some part at least, have been 
due to this diet. A mixed diet should contain all the nutri- 
ents in a digestible form and not too much hard indigestible 
material. 

The Relation of Work to Diet. — It has been shown experi- 
mentally that a man doing hard muscular work needs more 
food than one doing light work. The mere exercise gives the 
individual a hearty appetite; he eats more because he needs 
more of all kinds of food than if he were doing light work. Es- 
pecially is it true that the person of sedentary habits who gets 
little exercise should be careful not to overeat and to eat food 
that will digest easily. Protein food should also be reduced. 
Rich and hearty foods may be left for the man who is doing hard 
manual labor out of doors, who has a good digestion doubtless, 
and needs the energy for extra work 

The Relation of Environment to Diet. — We are all aware of 
the fact that the body seems to crave heartier food in winter 

HUNT- NEW &tf. — ^22 



The composition 
of a bottle of milk. 
Why is milk consid- 
ered a good food? 



330 



FOOD AND DIETARIES 




Table showing the cost of various foods. Using this table, make up an economi- 
cal dietary for one day, three meals, for a man doing moderate work. Give reasons 
for the amount of food used and for your choice of foods. Make up another 
dietary in the same manner, using expensive foods. What is the difference in your 
bill for the day? 



THE BEST DIET 



331 



than in summer. The temperature of the body is maintained 
at 98 J ° in winter as in summer, although much more heat is 
lost from the body in the cold weather. Hence in winter the 
heat-producing foods should be increased to provide for a greater 
supply of fuel and of energy because we exercise more in cold 
weather. We may use carbohydrates for this purpose, as they 
are economical and are digested more easily than fats. The 
inhabitants of cold countries get their heat-releasing foods 
largely from fats, because less plant food is produced there. 
In tropical countries and in hot weather little protein should 
be eaten and a considerable amount of fresh fruit should be used. 
Food Economy. — The American people are far less economical 
in their purchase of food than most other nations. Nearly one 
half of the total income of the 
average workingman is spent on 
food. He spends a large amount 
on food, partly because he wastes 
money in purchasing expensive and 
unnecessary foods. A comparison of 
the daily diets of persons in vari- 
ous occupations in this and other 
countries shows that as a rule we 
eat more than is requhed to sup- ^hree portions of food, each con- 

ply the necessary amount for fuel taining the same amount of nourish - 

and on repair, and that our work- ^^^ ' 

ingmen eat more than those' of other countries. Another waste 
of money by the American is in the false notion that a large 
proportion of the daily dietary should be meat. Many people 
think that the most expensive cuts of meat are the most 
nutritious. The falsity of this idea may be seen by a careful 
study of the table on page 330, compiled by Atwater, which 
shows the relative amount of various foods purchasable for 25 
cents. 

Daily Fuel Needs of the Body. — It has been pointed out 
that the daily diet should differ widely according to age, occu- 
pation, time of year, etc. A boy requires slightly more than a 
girl. The following table shows the daily fuel needs for several 
ages and occupations: — 




332 FOOD AND DIETARIES 

Daily Calorie Needs (Approximately) 
Obs. 

1. For child under 2 years 000 Calories 

2. For child 2-5 years 1200 Calories 

3. For child 6-9 years o 1500 Calories 

4. For child 10-12 years 1800 Calories 

5. For child 12-14 (woman, hght work also) 2100 Calories 

6. For boy (12-14), girl (15-16), man sedentary .... 2400 Calories 

7. For boy (15^16) (man, Hght muscular work) .... 2700 Calories 

8. For man, moderately active muscular work 3000 Calories 

9. For farmer (busy season) ......... 3200 to 4000 Calories 

10. For ditchers, excavators, etc 4000 to 5000 Calories 

11. For lumbermen, etc 5000 and more Calories 

Normal Heat Output. — We know that different amounts of 
energy are released by the body at different times and under 
different conditions. The following table gives the result of 
some experiments made to determine the hourly and daily 
expenditure of energy of the average normal grown person when 
asleep and awake, at work or at rest. 

Average Normal Output of Heat from the Body 



Conditions op Musctjlab Acttivitt 



Man at rest, sleeping . 

Man at rest, awake, sitting up 

Man at Ught muscular exercise 

Man at moderately active muscular exercise 

Man at severe muscular exercise 

Man at very severe muscular exercise . . 



Average 
Calories 
PER Hour 



65 Calories 
100 Calories 
170 Calories 
290 Calories 
450 Calories 
600 Calories 



It is very simple to use such a table in calculating the number 
of calories which are spent in twenty-four hours under different 
bodily conditions. For example, suppose the case of a clerk or 
school-teacher leading a relatively inactive life, who 

sleeps for 9 hours X 65 Calories = 585 

works at desk 9 hours X 100 Calories = 900 

reads, writes, or studies 4 hours X 100 Calories = 400 

walks or does light exercise 2 hours ... X 170 Calories = 340 

222d 



FOOD WASTE IN THE KITCHEN 333 

This comes out, as we see, very close to example 6 of the 
table ^ on page 332. 

How we may find whether we are eating a Properly Balanced 
Diet. — We already know approximately our daily calorie 
needs and about the proportion of protein, fat, and carbohydrate 
required. Dr. Irving Fisher of Yale University has worked out 
a very easy method of determining whether one is Hving on a 
proper diet or not. He has made up a number of tables, parts 
of which are shown on page 334,^ in which he has designated 
portions of food, each portion furnishing 100 calories of energy. 
The tables show the proportion of protein, fat, and carbohydrate 
in each food, so that it is a simple matter by using such tables 
to estimate the proportions of the various nutrients in our 
dietary. We may rely with safety upon a diet based upon 
either Atwater's, Chittenden's, or Voit's standard. From the 
tables on page 334 make out a simple dietary for yourself, first 
estimating your own needs in calories and then picking out 100 
calorie portions of food which will give you the proper propor- 
tions of protein, fat, and carbohydrate. 

Food Waste in the Kitchen. — Much loss occurs in the im- 
proper cooking of foods. Meats especially, when overdone, lose 
much of their flavor and are far less easily digested than when 
they are cooked properly. The chief reasons for cooking meats 
are that the muscle fibers may be loosened and softened, in 
which condition they are digested more easily, and that the 
bacteria and other parasites in the meat may be killed by the 
heat. The common method of frying makes foods difficult to 
digest. A good way to prepare meat, either for stew or soup, 
is to place the meat, cut in small pieces, in cold water, and 
allow it to simmer for several hours. Rapid boiUng toughens 
the muscle fibers just as the white of egg becomes solid when 
heated. BoiHng and roasting are excellent methods of cooking 
meat. In order to prevent the loss of the nutrients in roasting, 
it is well to baste the meat frequently; thus a crust is formed 
on the outer surface of the meat, which prevents the escape 
of the juices from the inside. 

^ The above tables and those which follow have been taken from the excellent 
pamphlet of the Cornell Reading Course, No. 6, Human Nutrition* 



334 



FOOD AND DIETARIES 



Tables of Food Values, Units and Weights 







Wrich T 

OF 100 

Calories 


C'aLoRIES 1'11RNI«HED By 


Name of Food 


Portion containing 
100 Calories 








Tiut. 


Pat, 


Carbo. 


1. Vegetable 




Ounces 








Crackers 


2 crackers 


.9 


10 


20 


70 


Wheat Dread 


Thick slice 


L3 


9 


7 


84 


Corn meal 


Cereal dish 


.90 


10 


5 


85 


(Jatmeal 


U" servings 


5.G 


18 


7 


75 


Beans (baked) 


Side dish 


2.66 


21 


18 


61 


Rice 


Cereal dish 


3.1 


10 


1 


89 


Sugar 


3 teaspoonfuls 


.86 


— 


— 


100 


Potatoes (boiled) 


1 large size 


3.62 


11 


1 


88 


Cabbage 


4 servings 


11 


20 


8 


72 


Tomatoes 


4 average servings 


15.2 


21 


7 


72 


Lettuce 


5 average servings 


18 


25 


14 


61 


2. Animal 












Beef (sirloin) 


Small steak 


1 + 


31 


69 


— 


Brisket 


Ordinary serving 


1.30 


42 


58 


— 


Mutton (leg) 


Large serving 


1.2 


35 


65 


— 


Pork (loin) 


Small serving 


.97 


18 


82 


— 


Ham 


Ordinary serving 


1.1 


28 


72 


— 


Veal (leg) 


Large serving 


2.4 


73 


27 


— 


Chicken 


Large serving 


3.2 


79 


21 


— 


Codfish 


2 servings 


4.9 


95 


5 


— 


Oysters 


1 dozen 


6.8 


49 


22 


29 


Lobster 


2 servings 


4.1 


78 


20 


2 


Eggs 


1 large egg 


2.1 


32 


68 


— 


3. Dairy products 












Whole milk 


Small glass 


4.9 


19 


52 


29 


Buttermilk 


1^ glasses 


9.7 


34 


12 


54 


Butter 


Small pat 


0.44 


0.5 


99.5 


— 


Cheese (Amer.) 


1| cubic inches 


.77 


25 


73 


2 


4. Fruits, nuts, etc. 












Bananas 


1 large 


3.5 


5 


5 


90 


Oranges 


1 large 


9.4 


6 


3 


91 


Watermelon 


1 whole 


27.0 


6 


6 


88 


Apples 


2 


7.3 


3 


7 


90 


Peanuts 


13 


.62 


20 


63 


17 


Chocolate 


I square 


.56 


8 


72 


20 



ADULTERATIONS IN FOODS 335 

Vegetables are cooked in order that the cells containing starch 
grains may be burst open. This allows the starch to be more 
easily reached by the digestive fluids. Inasmuch as water 
may dissolve out nutrients from vegetable tissues, it is best to 
boil them rapidly in a small amount of water. This gives less 
time for the solvent action to take place. Vegetables should be 
cooked with the outer skin left on when it is possible. 

Problem. To determine some forms of food adidterations. 
{Laboratory Manual, Proh. XLIII; Laboratory Problems, Prob. 
179.) 

Adulterations in Foods. — The addition of some cheaper or 
non-nutritious substance to a food, with the view to cheating 
the purchaser, or the replacing of some of the nutritive sub- 
stances with something less nutritious, is known as adulter- 
ation. One of the commonest adulterations is the substitution 
of grape sugar (glucose) for cane sugar. Most cheap candy is 
adulterated thus. Flour and other cereal foods are sometimes 
adulterated with some cheap substitutes, as bran or sawdust. 
Coffee, cocoa, and spices have been in the past subject to great 
adulteration; cottonseed oil is often substituted for olive oil; 
oleomargarine has been too frequently sold for butter; while 
honey, sirups of various kinds, cider and vinegar, have all 
been found to be either artificially made from cheaper substi- 
tutes or to contain such substitutes. Sausage may have a cheap 
cereal substituted for meat in it. 

Probably the food which suffers most from adulteration is 
milk, as water can be added without the average person being 
the wiser. By means of an inexpensive instrument known as 
a lactom'eter, this cheat may easily be detected. In most cities, 
the milk supply is carefully safeguarded, because of the danger 
of spreading typhoid fever from impure milk. Milk was formerly 
often treatei with preservatives which kill the bacteria in it 
and prevent the milk from souring rapidly. Such preservatives, 
as formaldehyde, are harmful to health. 

Pure Food Law. — • Thanks to tlie National Pure Food Law 
passed by Congress in 1906, and to the activity of various city 
and state boards of health, the opportunity to pass adulterated 



336 FOOD AND DIETARIEST 

foods on the public is now greatly lessened. This law, which 
does not work so well in the case of drugs and patent medicines, 
has prevented adulteration of many articles by setting up 
standards of purity for food products and by requiring proper 
labels on all goods put up in packages, such as canned goods, 
jams, jellies, etc. Thus we may at least know when we buy 
adulterated or artificially colored foods. The law also requires 
the inspection of all animal products shipped from one state 
to another. 

Impure Water. — Great danger comes from drinking impure 
water. This subject has already been discussed under Bacteria, 
where it was seen that the spread of typhoid fever in particular 
is due to a contaminated water supply. As citizens we must 
aid all legislation that will safeguard the water used by our 
towns and cities. Boiling water for ten minutes or longer will 
render it safe from all germs. 

Stimulants. — We have learned that food is anything that 
supplies building material or releases energy in the body; but 
some materials used by man, presumably as food, do not come 
under this head. Such are tea and coffee. When taken in 
moderate quantities, they produce a temporary increase in the 
vital activities of the person taking them, but they neither build 
tissue nor release energy and hence are stimulants, not foods. Tea 
and coffee when used in moderation often appear to be harm- 
less to adults, but they are sometimes stimulating and a few 
people cannot use either without ill effects, even in small quan- 
tity. It is the habit formed by relying upon the stimulation 
given by tea or coffee that makes them a danger to man. In 
large amounts, they are undoubtedly injurious because of a 
stimulant called caffeine (kaf'e-in) in coffee and the'ine in tea. 
Cocoa and chocolate, although both contain a stimulant like 
caffeine, are in addition good foods, having from 12 per cent 
to 21 per cent of protein, from 29 per cent to 48 per cent fat, 
and over 30 per cent carbohydrate in their composition. 

Is Alcohol a Food? — The question of the use of alcohol has 
been of late years a matter of absorbing interest and importance 
among physiologists. A few years ago Dr. At water performed 
a series of very careful experiments by means of the respiration 



ALCOHOL 337 

calorimeter, to ascertain whether alcohol is of use to the body- 
as food or not. ^ In these experiments the subjects were given, 
instead of their daily allotment of carbohydrates and fats, 
enough alcohol to supply the same amount of energy that these 
foods would have given. The amount was calculated to be 
about two and one half ounces per day, about as much as 
would be contained in a bottle of light wine.^ This alcohol was 
administered in small doses six times during the day. Professor 
Atwater's results may be summed up briefly as follows : — 

1. The alcohol administered was almost all oxidized in the 
body. 

2. The potential energy in the alcohol was transformed into 
heat or muscular work. 

3. The body did about as well with the rations including 
alcohol as it did without it. 

The committee of fifty eminent men appointed to report on 
the physiological aspects of the drink problem reported that a 
large number of scientific men stated that they were in the habit 
of taking alcoholic liquor in small quantities, and many reported 
that they did not feel harm thereby. A number of scientists 
seem to agree that when taken in small quantities alcohol may 
be a kind of food, although a very poor kind. 

On the other hand, we know that although alcohol may tech- 
nically be considered as a food, it is very unsatisfactory and, 
as the following statements show, it has a harmful effect on 
the nervous system which foods do not have. 

Alcohol a Poison. — A commonly accepted definition of a poison 
is that it is any substance which, when taken into the body, tends 
to cause the death or serious detriment to the health of the organism. 
That alcohol may do this is well known by scientists. A 
study of the causes of death in the vital statistics of state or 
city shows a surprisingly large number of deaths from alcoholism, 

^ Alcohol is made up of carbon, oxygen, and hydrogen. It is very easily 
oxidized, but it cannot, as is shown by the chemical formula, be of uss to the 
body in tissue building, because of its lack of nitrogen. 

^ Alcoholic beverages contain the following proportions of alcohol : beer, 
from 2 to 5 per cent; wine, from 8 to 20 per cent; liquors, from 30 to 70 per 
cent. Patent medicises frequently contain as high as 45 per cent alcohol. 
(See page 340.) 



338 FOOD AND DIETARIES 

in spite of the Eighteenth Amendment. And now that home- 
made substitutes for the more carefully manufactured alcoholic 
drinks are consumed b}" hundreds of thousands of lawbreakers, 
the chances of alcoholic poisoning are very great. 

Taken in small quantities alcohol acts as a quick stimulant. 
In large quantities it is a narcotic and paralyzes the nervous 
system. 

But a more serious charge against alcohol is that it acts as 
a habit-forming drug. People who '^ get the craving " unfor- 
tunately cannot break away easily from the overwhelming 
desire to drink. This habit results all too often in degradation 
and death. 

Dr. Kellogg, of the Battle Creek Sanitarium, points out that 
strychnine, quinine, and many other drugs are oxidized in the 
body, but sureh^ cannot be called foods. The following reasons 
for not considering alcohol a food are taken from his writings : — 

"1. A habitual user of alcohol has an intense craving for his accus- 
tomed dram. Without it he is entirely unfitted for business. One never 
experiences such an insane craving for bread, potatoes, or any other par- 
ticular article of food. 

" 2. By contmuous use the body acquires a tolerance for alcohol. 
That is, the amount which may be imbibed and the amount required to 
produce the characteristic ejBPects first experienced graduall}" increase 
until veny great quantities are sometimes required to satisfy the craving 
which its habitual use often produces. This is never the case with true 
foods. . . . Alcohol behaves in this regard just as does opium or any other 
drug. It has no resemblance to a food. 

"3. When alcohol is withdra\\'n from a person who has been accus- 
tomed to its dail}^ use, most distressing effects are experienced. . . . \Yho 
ever saw a man's hand trembling or his nervous system unstrung because 
he couLl not get a potato or a piece of cornbread for breakfast ? In this 
respect, also, alcohol behaves like opium, cocaine, or any other enslav- 
ing chug. 

'' 4. Alcohol lessens the appreciation and the value of brain and nerve 
activity, while food reenforces nervous and mental energy. 

" 5. Alcohol as a protoplasmic poison lessens muscular power, whereas 
food increases energy and endurance. 

"6. Alcohol lessens the power to endure cold. This is true (o such a 
marked degree that ils use by persons accoinpaiiyiiig Arctic expeditions 
is absolutely j^roliibited. ImxxI, on the other lisiud, increases ability to 
endure cold. The temperature after taking food is raised. After taking 
alcohol, the temperature, as shown by the thermometer, is lowered. 



TOBACCO 



339 



" 7. Alcohol cannot be stored in the body for future use, whereas all 
food substances can be so stored. 

" 8. Food burns slowly in the body, as it is required to satisfy the 
body's needs. Alcohol is readily oxidized and eliminated, the same as 
any other oxidizable drug." 

The Use of Tobacco. — A well-known authority defines a nar- 
cotic as a substance 
'' wkich directly in- 
duces sleep, blunts the 
senses, and, in large 
amounts, produces 
complete insensibil- 
ity." Tobacco, opium, 
chloral, and cocaine 
are examples of nar- 
cotics. Tobacco owes 
its narcotic influence 
to a strong poison 
known as nicotine, 
the use of which in 
killing insect parasites 
on plants is well 
known. In experi- 
ments with jellyfish 
and other lowly organized animals, the author has found as 
small a quantity as one part of nicotine to one hundred thousand 
parts of sea water to be sufficient to affect profoundly an animal 
placed within it. The illustration here given shows its effect 
upon a fish. Nicotine in a pure form is so powerful a poison 
that two or three drops would be sufficient to cause the death 
of a man by its action on the nervous system, especially the 
nerves controlling the beating of the heart. 

The action of tobacco is well known among boys training for 
athletic contests. The heart is affected and boys become '' short- 
winded " as a result. The brain becomes stupefied and incapa- 
ble of doing its best work. It has been demonstrated that 
tobacco has an important effect also on muscular development, 
as shown by the stunted appearance of the young smoker. 




Experiment (by Davison) to show how tobacco 
affects the nervous system. The nicotine caught 
in the water by passing through it the smoke from 
six cigarettes, was sufficient to kill the fish in the jar. 



340 



FOOD AND DIETARIES 



The West Point and Annapolis academies forbid the use of 
tobacco, and college coaches insist that men training for the 
teams shall not use it. Investigations made on college students 
show that groups of smokers matched against non-smokers were 
found to do poorer work in their studies, to graduate at a later 
date, and to grow more slowly. The use of tobacco is asso- 
ciated with lack of application and of ambition. The college 
cigarette fiend is usually the college loafer. 

There is very complete agreement among teachers of boys 
below college age that the use of tobacco is very harmful and 
should at least be left alone until the boy is full grown. 

Problem, — A study of some medical frauds. (Laboratory 
Manual, Prob. XLIV; Laboratory Problems, Probs. 180-183.) 

Use and Abuse of Drugs. — The American people are ad- 
dicted to the use of drugs and, especially, patent medicines. A 




The amounts of alcohol in some liquors and in some patent medicines. 
A, beer, 5%; B, elaret, 8%; C, champagne, 9%; D, whiskey, 50%; E, well-known sarsapa- 
rilla, 18%; F, G, /f, much-advertised nerve tonics, 14%, 18%, 12%; 7, another much-adver- 
tised earsaparilla, 18%; J, a well-known tonic, 14%; K, L, bitters, 20%, 25% alcohol. 

glance at the street car advertisements shows this. Most of 
the medicines advertised contain alcohol in greater quantity 
than beer or wine, and many of them have opium, morphine, 
or cocaine in their composition. These drugs, in addition to 
being harmful, affect the person using them in such a manner 
that he soon feels the need for the drug. Thus the drug habit 
is formed, — a condition which has wrecked thousands of lives. 



USE AND ABUSE OF DRUGS 841 

The American Medical Association, by means of its publi- 
cations, is doing a great work in showing the public some of 
the frauds which are practiced by the patent medicine interests. 
It is shown, for example, that most cough medicines (or, as they 
used to be known, consumption cures) contain heroin or other 
habit-forming drugs, or else alcohol enough to act as a " bracer '^ 
and thus delude the poor victim into thinking he is better. A 
great number of the bitters or sarsaparillas contain enough 
alcohol to make them sought after in these days of prohibi- 
tion. Some patent medicines, especially those with trade names, 
are simply fakes and the buyer pays $1.00 or more for materials 
that could be purchased in the drug store for a few cents. 

A good rule to observe with reference to patent medicines 
is not to use any unless ordered to do so by a rehable physi- 
cian. It is time that the thinking American pubKc should wake 
to the fact that it is not only being cheated but also harmed 
physically by the patent medicines of which it is so fond. 

Summary. — Certain nutrients, organic or inorganic, form the 
basis of aD. foods. The organic nutrients are carbohydrates, 
fats or oils, proteins, and vitamins. The first two groups con- 
tain the elements C, H, O — protein contains N also. Examples 
of proteins are meats and eggs; of carbohydrates, cereals and 
most vegetables; of fat, butter. There are also mineral salts 
and mysterious substances known as vitamins which make up 
an essential part of a dietary. 

It has been determined that a mixed diet is necessary to sup- 
port Hfe; besides a proportion of the organic nutrients, it must 
contain inorganic salts as weU. 

Problem Questions. — 1. What is a food? 

2. What is a calorie? How is it determined? 

3. What is a balanced diet? Give examples. 

4. Why are certain vegetables included in a balanced diet ? 

5. What are cheap foods? Expensive foods? Give examples. 

6. What are the daily calorie needs and how are they 
determined ? 

7. Give some standards for a well-balanced diet. 

8. What is a 100 calorie portion? Illustrate. 

9. Describe the Pure Food Act of 1906. 



342 FOOD AND DIETARIES 

10. What is an adulterant? Is adulterated food always 
harmful ? 

11. Is alcohol a food? Is it a poison? 

12. Why are patent medicines harmful? 

Problem and Project References 

Allen, Civics and Health. Ginn and Company. 

Broadhurst, Home and Community Hygiene. J. B. Lippincott Company. 
Bulletin 13, American School of Home Economics, Chicago. 
Cornell University Reading Course, Bulletins 6 and 7, Human Nutrition, 
Davison, The Human Body and Health. American Book Company 
Fisher and Fisk, How to Live. Funk and Wagnalls. 
Harrow, Vitamines. E. P. Button and Company. 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 
Hunter and Whitman, Civic Science. American Book Company. 
Lusk, Science of Nutrition. W. B. Saunders Company. 
Nostrums j,nd Quackery. American Medical Association. 
Rose, Feeding the Family. The Macmillan Company- 
The Great American Fraud. American Medical Association. 
Sharpe, A Laboratory Manual. American Book Company. 
Stiles, Human Physiology. W. B. Saunders Company. 

U.S. Dept. of Agriculture, Farmers' Bulletins No. 23, 34, 42, 85, 93, 121. 132. 
142, 182, 249, 295, 298, 881, 903, and others (see list of titles). 



XXV. DIGESTION AND ABSORPTION 



Mouth 

Tongue 

ThroatL 



Purpose of Digestion. — We have learned that the starch and 
protein food of plants is formed in the leaves. A plant, how- 
ever, is unable to make use of the food in this condition. Be- 
fore it can be transported from one part of the plant body to 
another, it is changed into 
a soluble form. Much the 
same condition exists in an- 
imals. In order that food 
may be of use to man, it 
must be changed into a sol- 
uble form that will allow 
its passage through the walls 
of the alimentary canal, or 
food tube. Digestion consists 
in the changing of foods from 
an insoluble to a soluble form, 
so that they may pass through 
the walls of the alimentary 
canal and become part of the 
blood. 




Gullet 

Liver- 

Oall 

Bladder- 

BileDuct 

Pancrea^ 

Large 

Intestine 

Small 
Intestine- 

Appendlx^ 
Rectum 



Problem, — &tudy of the 
digestive system of a frog in 
order better to understand that 
of man. (Laboratory Manual, 
Prob. XLV; Laboratory 
Problems, Probs. 184 to 186.) 

Alimentary Canal. — In 
all vertebrate animals, including man, food is normally taken 
in the mouth and passed through a food tube during the process 
of digestion. This tube is composed of different portions, named, 

343 



Organs of Digestion. 



344 



DIGESTION AND ABSORPTION 



respectively, as we pass from the mouth, posteriorly, the gullet, 
stomach, and small and large intestine. 

Glands. — In addition to the alimentary canal proper, we 
find a number of digestive glands, varying in size and position 

connected with the canal 
As we have already 
learned, a gland is a col- 
lection of cells which 
takes up materials from 
the blood and pours them 
out as a secretion. They 
are like the nectar glands 
of a flower. 

Certain substances 
called enzymes, formed by 
glands, cause the digestion 
of food. The enz^mies are 
made in the cells of the 
glands and poured out 
with the fluid secretion 
into the food tube, where 
they act upon insoluble 
foods and change them 
to a soluble form. 

Structure. — The walls 
of the food tube are mus- 
cular and composed of long fibers which run lengthwise and 
small circular fibers passing Kke rings around the tube. The 
contraction of these muscles is very important in regulating the 
movement of the food. The entire inner surface of the food 
tube is covered with a soft lining of mu'cous membrane. This 
is always moist because certain cells, called mucus cells, empty 
their contents into the food tube, thus lubricating its inner 
surface. Where a large number of secreting cells are collected 
together, the surface of the food tube becomes indented to form 
a pitlike gland. Often such depressions are deep and branched, 
thus giving a greater secreting surface, as is seen in the Figure. 
The ceUs of the gland are always supplied with blood vessels and 




Diagram of a gland: i, the common tube 
which carries off the secretions formed in the 
cells Uning the cavity c; a, arteries carrying 
blood to the cells; v, veins taking blood 
away from the cells. 



THE DIGESTIVE SYSTEM 



345 



nerves, for the secretions of the glands are under the control of 
the nervous system. Think of a sour pickle and note what 
happens. 

Attached to the digestive tract of man are found the salivary 
glands in the walls of the mouth, gastric glands in the walls of 
the stomach; the liver and the pan'creas, two large glands which 
empty into the small intestine just below the stomach, and 
intestinal glands in the walls of the intestine. 

It will be the purpose of this chapter to follow the various 
food substances as they pass through the food tube in order 
to find how and where the changes take place in the various 
nutrients which prepare them to become part of the blood. 

Mouth Cavity in Man. — In our study of a frog we found 
that the mouth cavity has two unpaired tubes and four ar- 
ranged in pairs leading 
from it. These are (a) 
the gullet or food tube, 
(b) the windpipe (in the 
frog opening through the 
glottis), (c) the paired 
nostril holes (posterior 
nacres), (d) the paired 
Eustachian (ti-sta'-ki-an) 
tubes, leading to the ear. 
All of these openings are 
found in man. 

The roof of the mouth 
is formed in front by a 
plate of bone called the 
hard palate, and in back by a softer continuation called 
the soft palate, which separate the nose cavity from that of the 
mouth. That part of the space back of the soft palate is called 
the phar'ynx, or throat cavity, from which pass out the gullet and 
the windpipe. The lower part of the mouth cavity is occupied 
by a muscular tongue. Examination of its surface with a looking- 
glass shows it to be almost covered in places by tiny projections 
called papiVlce. These papillae contain organs known as taste buds, 
the sensory endings through which we determine the taste of sub- 

0UKT. NEW E8. 23 




Mouth cavity of man. 



346 



DIGESTION AND ABSORPTION 



stances. The tongue is used in moving food about in the 
mouth, in starting it on its way to the gullet, and plays an 
important part, as we know, in speaking. 

The Teeth. — The thirty-two teeth of man are divided, ac- 
cording to their functions, into four groups. In the center of 

each jaw in front are found 
four teeth with chisel-like 
edges; these are the inci'sors, 
or cutting teeth. On each end 
of these groups is found a 
single tooth, four in all, with 




-rX 3 2^ rather sharp points; they are 
i J i, l\yQ canines; look for them in 
a cat or dog. Two teeth on 
each side, back of these, eight 
in all, are called premolars. 
Lastty, beyond the premolars 
are the flat-top inolars, or grind- 
The teeth on the right side of both i^g teeth, of which there are 

jaws: 1, 2, incisors; 3, canines; 4, 5, pre- gix in each jaw. Food is CaUght 
molars; 6, 7, 8, flat-top molars. , . . -, • j • 

between irregular projections 
on the surface of the molars and crushed to a pulpy mass. 

Care of the Teeth. — Form the habit earl}^ in hfe of brush- 
ing the teeth upon getting up in the morning and just before 
going to bed at night. A ver- 
tical movement of the brush C^otr^- 
should be used between the /\/gc/c 
teeth so as to dislodge bits of 
food caught there. The gums b^q*., 
should be brushed as well so 
as to help the circulation of the 

blood there. A weak acid tooth Longitudinal section of a tooth (a 

wash, made of equal parts of flat-top molar). 

vinegar and water, is helpful, as is a powder containing ground 

pumice. Can you see the use of each of these? 

Internal Structure of a Tooth. — If a tooth is cut lengthwise, it is found 
to be hollow; this cavity, called the pulp cavity, corresponds to the cavity 
containing marrow in bones. In life it contains living material — the blood 




■Enamel 

Dentine 

Root canal or 
nerve chamber 



THE DIGESTIVE SYSTEM 



347 



vessels, nerves, and cells which build up the bony part of the tooth. The 
bulk of the hard part of the tooth consists of a limy material called den- 
tine (den'tin). Outside of this is a very hard substance called enamel; 
this substance, the hardest in all the body, is thickest on the exposed 
surface or crown of the tooth. Each tooth is held in its place in the 
jawbone by a thin layer of bony substance called cement. : 

Problem. — How foods are chemically prepared for absorp- 
tion into the blood. (Laboratory Manual, Prob. XLVI; Labo- 
ratory Problems, Probs. 187 to 193.) 

(a) In the mouth. 

(6) In the stomach. 

(c) In the small intestine. 

Salivary Glands. — We are all familiar with the substance 
called saliva which acts as a lubricant in the mouth. Saliva is 
manufactured in the cells of three pairs of glandS which empty 
into the mouth, and which are called, according to their posi- 
tion, the parot'id (under the ear), 
the submaxillary (under the jaw- 
bone), and the sublin'gvxil (under 
the tongue). 

Digestion of Starch. — If we 
collect some saliva in a test tube, 
add to it a little starch paste, 
place the tube containing the 
mixture for twenty minutes in 
tepid water, and then test with 
Fehling's solution, we shall find 
grape sugar present. Careful tests 
of the starch paste and of the 
saliva made separately will usu- 
ally show no grape sugar in either. Experiment showing non-osmosis 

If another test be made for of starch and water in tube A and 

grape =ugar, aftw starch paste, osmosis of sugar solution in tube B. 
saliva, and a few drops of any weak acid have been mixed for 
twenty minutes, the starch will be found not to have changed. 
The digestion of starch to grape sugar is caused by the presence 
in the saliva of an enzyme, or digestive ferment. You remem- 
ber that starch in the growing corn grain was changed to grap^ 




348 DIGESTION AND ABSORPTION 

sugar by an enzyme called diastase. Here the same action is 
caused by an enzyme called ptyalin (tfa-lin). This ferment, as we 
can prove, acts only in a slightly alkaline or neutral medium at 
about the temperature of the body. 

How Food is Swallowed. — After food has been chewed and 
mixed with saUva, it is rolled into little balls and pushed by the 
tongue into such position that the muscles of the throat cavity 
may seize it and force it downward. Food, in order to reach 
the gullet from, the mouth cavity, must pass over the glottis, the 
opening into the windpipe or trachea. When food is in the course 
of being swallowed, the upper part of this tube forms a trap- 
door, called the epiglot'tis, over the opening. When this trap- 
door is not closed, and food '' goes down the wrong way," we 
choke, and the food is expelled by coughing. 

The Gullet, or Esophagus. — In man this part of the food 
tube is much longer proportionately than in the frog. Like the 

rest of the food tube it is 
lined by soft and moist 
mucous membrane. The 
wall is made up of two 

Peristaltic waves in the gullet of man: h, bo- sets of muscles, — the in- 
ius or little baU of food. • i • j 

side ones runnmg around 
the tube; the outer band of muscle taking a longitudinal course. 
After food leaves the mouth cavity, it gets beyond our direct 
control, and the muscles of the gullet, stimulated to activity by 
the presence of food in the tube, push the food down to the 
stomach by a series of penstaVtic contractions. The gullet passes 
directly through a muscular partition, the diaphragm (di'a- 
fram), which is lacking in the frog. The diaphragm sepa- 
rates the heart and lungs from the other organs of the body 
cavity. 

Stomach. — The stomach is a pear-shaped organ capable of 
holding about three pints. The end opposite to the gullet, 
which empties into the small intestine, is provided with a 
ring of muscle forming a valve called the pylo'rus. 

Gastric Glands. — The inner wall of the stomach has long folds 
which run lengthwise. Between the folds are tiny pits, or the 
openings of the gastric glands which lie imbedded in the wall of 




DIGESTION 



349 



isophagus- 




PancreaticDuct 



stomach and beginning of small intestine. 



the stomach. The gastric' glands are little tubes, the lining of 
which secretes the gastric juice, sl fluid which is poured into the 
stomach to assist in the 
digestion of food. This 
fluid is largely water. It 
is slightly acid in its chem- 
ical reaction, containing 
about 0.2 per cent free 
hydrochloric acid. It also Bile Duct ^^ 
contains a very important 
enzyme called pepsin, and 
another less important one /«/-^5f;«^J 
called rennin. 

Action of Gastric Juice. 
— If protein is treated 
with artificial gastric juice 
at the temperature of the 

body, it will be found to become swollen and then gradually 
to change to a substance which is soluble in water. Most 

protein substances are insoluble 
and contain amino-acids which 
are separated by digestion. These 
amino-acids are used in building 
up the cells of the body and even- 
tually become protoplasm. 

One enzyme of gastric juice, 
called rennin, curdles or coagu- 
lates a protein found in milk; 
after the milk is curdled, the pepsin 
is able to act upon it. " Junket " 
tablets, which contain rennin, are 
used in the kitchen to cause this 
change. 

The hydrochloric acid found in 
the gastric juice acts upon lime 
and some other salts taken into the stomach with food, 
dissolving them so that they may pass into the blood and even- 
tually form the mineral part of bone or of other tissue. 







Section through wall of the stom- 
ach, much magnified: A, gastric 
glands; B, muscular fibers. 



350 DIGESTION AND ABSORPTION 

Hormones and their Work. — The modern study of physiology 
is fascinating because we are just beginning to find causes for 
some of the conipUcated actions that go on in the body. Many 
of the happenings, sucii as the secretion of gastric juice at a time 
when it will do the most good (when food is in the stomach), 
seems to be brought about by a substance formed in some of the 
cells lining the walls of the stomach. This substance is one of a 
group of mysterious regulative agents called hormones (hor'monz). 
They are formed in groups of gland cells (the ductless glands) 
or in cells scattered throughout other organs, as in the walls of 
the stomach and intestine and in the pancreas and liver. The 
secretions, however, reach the blood stream and are carried to 
various parts of the body. The regulative action of different hor- 
mones is undoubtedly the factor which causes growth of various 
parts of the body and promotes the smooth running of a series of 
events which take place, for example, in digestion. Here one 
organ after another takes up the work of digesting its part of the 
meal, the initiative to do this work at the right moment being 
brought about by different hormones, which, at just the right 
moment, call the gland cells to do their work. 

Movements of the Stomach. — The stomach walls are mus- 
cular and as soon as food reaches the stomach the action of 
these muscles begins and keeps the food in constant motion. 
Thus the food is gradually mixed with gastric juice and some 
digestion takes place. These movements are of much use 
in softening and breaking up the food and when it finally 
leaves the stomach it is in a semi-fluid condition with few 
large lumps of undigested matter. When food is thoroughly 
acidulated by means of the gastric hydrochloric acid, the ring 
of muscle around the pyloric end of the stomach relaxes and 
little gushes of food are allowed to pass into the small intestine. 
As soon as this acid substance strikes the walls of the small in- 
testine a hormone made there is at once released into the blood, 
and the liver and the pancreas are made to pour out their 
digestive fluid. 

The Pancreas. — The pancreas, a diffuse gland opening into 
the small intestine just below the pylorus, is one of the most 
important digestive glands of the body 



DIGESTION 



351 



Starch added to artificial pancreatic fluid and kept at blood 
heat is soon changed to sugar. Proteins, under the same con- 
ditions, are separated into amino-acids. Fats, which so far have 
been unchanged except to be melted by the heat of the body, 
are changed by the action of the pancreas into a form which 
can pass through the walls of the intestine. These changes are 
brought about by means of three enzymes: amylop'sin, which 
acts upon starches, trypsirij 
which acts upon proteins, and 
lip'ase or steap'sin, which acts 
upon fats. Pancreatic fluid 
also contains a milk-curdling 
enzjnue. If we test pancreatic 
fluid we find it strongly alka- 
line in its reaction. If two 
test tubes, one containing 
olive oil and water, the other 
olive oil, water, and a weak 
solution of caustic soda, an 
alkali, be shaken violently 
and then allowed to stand, 
the oil and water will quickly 
separate, while the oil, caustic 
soda, and water will remain 
for some time in a milky 
emulsion. Pancreatic fluid 
similarly emulsifies fats and changes them into soft soaps and 
fatty acids in which form they may be absorbed. 

Liver. — The liver is the largest gland in the body. It is of 
a deep red color. In man it hangs just below the diaphragm, 
a little to the right side of the body. It is divided into three 
lobes, between two of which is the gall bladder, a thin-walled 
sac which holds the bile, a secretion of the liver. Bile is a 
strongly alkaline fluid of golden brown color which becomes 
green on exposure to the air. It reaches the intestine through 
a common opening with the pancreatic fluid. Almost one quart 
of bile is passed daily into the intestine. 

Functions of Bile. — The same hormone which causes 




Milk, a form of emulsion, as seen under 
the microscope. The tat globules appear 
in groups. In the circle one group is 
highly magnified. 



352 DIGESTION AND ABSORPTION 

the secretion of pancreatic fluid also causes the flow of bile. 
The most important function of bile seems to be assisting the 
pancreatic juice to digest and absorb fats. If two funnels,, 
each containing filter paper, one moistened with bile, and 
the other dry, be filled with oil, the oil will be found to pass 
through the moistened filter paper with much greater ease 
than thi'ough the dry one. Bile is shghtly antiseptic and thus 
may help prevent fermentation within the intestine b}^ keeping 
down the growth of bacteria. 

Formation of Glycogen. — Perhaps the most important func- 
tion of the Uver is the formation of a material called gly'cogen, 
or animal starch. A large amount of blood received by the liver 
comes directly from the walls of the stomach and intestine, 
so that the Uver normally contains about one fifth of all the 
blood in the bod3^ This blood is very rich in food materials, 
and from it the cells of the fiver take out materials necessar}^ to 
form glycogen, which is then stored in the Hver. When food 
which can be oxidized quickly is needed, the gh'cogen is 
changed to sugar and carried off by the blood to the tissues 
which require it, and there used for this purpose. Gl3T0gen is 
also stored in the muscles, where it is oxidized to release energy 
when the muscles are exercised. 

Small Intestine. — The process of digestion is carried on not 
only in the mouth and stomach, but also in the small intestine. 
This organ is described on the following page, in connection 
with absorption. In the waUs of the small intestine are numerous 
small intestinal glands which pour their secretions into the tube 
and assist the pancreatic fluid in digesting starch, protein, and 
oils. 

Problem. — A study to determine where and how digested foods 
pass into the blood. (Laboratory Manual, Prob. XLVII; Labo- 
ratory Problems, Probs. 194 to 197.) 

The Absorption of Digested Food into the Blood. — The ob- 
ject of digestion is to change foods from an insoluble to a 
soluble form. This has been seen in the study of the action of 
the various digestive fluids in the body, each of which aids in 
dissolving solid foods, and, in case of the bile, actually assist- 



ABSORPTION OF FOODS 



353 



ing them to pass through the walls of the intestine. A small 
amount of digested food is absorbed by the blood in the walls 
of the stomach. Most of the absorption, however, takes place 
through the walls of the small intestine. 

Structure of the Small Intestine. — The small intestine in man 
is a slender tube nearly twenty feet in length and about one 
inch in diameter. Its walls contain muscles which, by a series 
of slow waves of contraction, force the material within gradually 
toward the posterior end. The 
peristaltic movements of the mus- 
cles of the coats are of very great 
importance in the process of ab- 
sorption, and these movements 
are caused to a great extent (as is 
the secretion of the various glands 
of the digestive system) by the 
mechanical stimulus of the food 
within the food tube. As one 
function of the small intestine is 
absorption, we must look for 
adaptations which increase the 
absorbing surface of the tube. 

This is gained in part by the diagram of a bit of the wall of 
inner surface of the tube being the small intestine, greatly magni- 
,1 • X X r 1 J fied. a, mouths of . intestinal 

thrown mto transverse folds ^^^^^^. ^^ ^^^ ^^^ lengthwise to 
which not only retard the rapid- show blood vessels and lacteal 
ity with which food passes down bmnchTs^'to'oth^r !Sih!'\\ kTtes?? 

the intestine, but also give more nal glands; m, artery; V, vein; 
1 1 • r; T) 4. r I, t, muscular coats of intestine 

absorbmg suriace. But tar more ^^^ 

important for absorption are 

millions of little projections called villi (singular, villus), which 

cover the inner surface of the small intestine. 

The Villi. — So numerous are these projections that the whole 
surface presents a velvety appearance. The villi form the chief 
organs of absorption in the intestine, several thousand being 
distributed over every square inch of surface. By means of 
the folds and the villi the small intestine is estimated to have 
an absorbing surface equal to twice that of the surface of the 




354 



DIGESTION AND ABSORPTION 



arm 



body. The internal structure of a villus is best seen in a longi- 
tudinal section. The outer wall is made up of a thin layer of 
cells which absorb the digested food from within the intestine. 
Underneath these cells Hes a network of very tiny blood ves- 
sels, while inside of these, occupying the core of the villus, are 
found spaces which, because of their white appearance after 
the absorption of fats, have been called lac'teals. 

Absorption of Foods. — Food substances in solution pass by 
osmosis into the cells Hning the villi. These cells are alive, and 

therefore have the power of selecting 
certain substances and rejecting others. 
Once within the villi, the sugars and 
digested proteins pass through tiny blood 
vessels into larger vessels comprising the 
portal circulation. These pass to the 
liver, where, as we have seen, sugar is 
taken from the blood and stored as 
glycogen. From fche liver, the food in 
the blood is carried to the heart, from 
there is pumped to the lungs, returns 
to the heart, and is pumped to the 
tissues of the body. A large amount 
of water and some salts also are ab- 
sorbed through the walls of the stomach 
and intestine. The fats in the form 
of soaps and fatty acids pass into the 
cells Uning the walls of the villi but 
are immediately changed back to fats, 
Diagram to show how the in which form they are found in the 

nutrients reach the blood. ^^^^^^^ ^^^^^^ ^.^j^-^^ ^^^ ^.jlj^ ^Sits 

eventually reach the blood by way of the thoracic duct without 
passing through the liver. 

Large Intestine. — The large intestine has somewhat the 
same structure as the small intestine, except that the diameter 
is greater and it has no villi. Considerable absorption, how- 
ever, takes place through its walls as the mass of food and 
refuse material is slowly pushed along by the muscular walls. 

In this portion of the intestine live millions of bacteria. 




HYGIENIC HABITS OF EATING 355 

some of which manufacture poisonous substances from the 
foods on which they Hve. These substances are easily ab- 
sorbed through the walls of the large intestine, and passing 
into the blood, cause headaches or sometimes serious trouble. 
Hence it follows that the lower bowel should be emptied of 
this matter at least once a day. Constipation is one of the 
serious evils the American people have to deal with, and it is 
largely brought about by the artificial life which they lead, with 
its lack of sufficient exercise, fresh air, and sleep. 

Vermiform Appendix. — At the point where the small in- 
testine widens to form the large intestine, a baglike pouch is 
formed. From one side of this pouch is given off a small 
tube about four inches long, closed at the lower end. This 
tube, the function of which in man is unknown, is called the 
vermiform appendix. It has come to have unpleasant noto- 
riety in late years, as the seat of serious inflammation. It 
often becomes necessary to remove the appendix in order to 
prevent this inflammation from spreading to the surrounding 
tissues. 

Hygienic Habits of Eating; the Causes and Prevention of 
Dyspepsia. — From the contents of the foregoing chapter it 
is evident that the object of the process of digestion is to break 
up solid food so that it may be absorbed to form part of the 
blood. Any habits we may form of thoroughly chewing our 
food will aid in this process. Much of the distress known as 
dyspepsia is due to eating too rapidly with consequent lack of 
proper mastication of food. The message of Horace Fletcher in 
bringing before us the need of proper mastication of food and 
the attendant evils of overeating is one which we cannot afford 
to ignore. It is a good rule to go away from the table feeling 
hungry. Eating too much overtaxes the digestive organs and 
prevents their working to the best advantage. Still another 
cause of dyspepsia is eating when in a fatigued condition. It 
is always a good plan to rest a short time before eating, es- 
pecially after any hard manual work. Eating between meals 
is also condemned by physicians because it calls the blood to 
the digestive organs at a time when it should be in other parts 
of the body. 



356 DIGESTION AND ABSORPTION 

Effect of Alcohol on Digestion. — It is a well-known fact 
that alcohol extracts water from tissues with which it is in con- 
tact. This fact works much harm to the interior surface of 
the food tube, especially the walls of the stomach, which in 
the case of a hard drinker are likely to become irritated and 
much toughened. In small amounts alcohol stimulates the se- 
cretion of the salivary and gastric glands, and thus seems to 
aid in digestion. It is doubtful, however, whether this aid is 
real. 

Experiments on dogs performed by Chittenden show that 
alcohol retards digestion. He fed dogs on meat with water and 
then on meat with very dilute alcohol. The meat with alcohol 
took on the average about 25 minutes longer to digest. 

Summary. — The organs of digestion form a tube, the walls 
of which are lined with digestive glands. Muscles are also 
found in the walls of the food tube; they cause an almost 
constant churning movement in the stomac/ , and are also re- 
sponsible for the movements known as peristalsis in the small 
intestine. 

Digestion is a process which causes insoluble food to pass 
through a series of changes so that it becomes simpler in struc- 
ture and will pass through the walls of the food tube. Diges- 
tion is brought about by the action of various enzymes, each 
of which acts upon a given substance. 

Absorption takes place largely in the small intestine, where 
many fingerlike projections called villi take up the various food 
substances and pass them into the blood. Fats are not taken 
directly into the blood but are first passed through tubes called 
the ladeals. Eventually they reach the blood througli the 
thoracic duct. 

Problem Questions. — 1. How is digestion brought about? 

2. What is an enzyme? How is it made? Name some 
enzymes and give their functions. 

3. Discuss the teeth as to function, structure, and care. 

4. What is the function of the tongue in digestion? of the 
salivary glands? 

5. What are the functions of the stomach? How are they 
accomplished? 



DIGESTION 357 

6. What are hormones and what do they do? 

7. Why is the pancreas considered the most important di- 
gestive gland? 

8. What is glycogen and where is it made? 

9. How and where is food absorbed? 

10. What effect does alcohol have on digestion? 

Problem and Peoject References 

Burton-Opitz, A Textbook of Physiology. W. B. Saunders Company. 

Howell, Human Physiology. 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Hunter and Whitman, Civic Science. American Book Company. 

Martin, Human Body. Henry Holt and Company. 

Starling, Principles of Human Physiology. Lea and Febiger. 

Sharpe, A Laboratory Manual. American Book Company, 

Stiles, Nutritional Physiology. W. B. Saunders Company. 



XXVI. THE BLOOD AND ITS CIRCULATION 

Problem. To study the composition of the blood. (Labora- 
tory Maniml, Prob. XLVIII; Laboratory Problems, Probs. 
198 to 200.) 

Functions of the Blood. — The chief function of the digestive 
tract is to change insoluble foods to such form that they can be 
absorbed through the walls of the food tube and become part of 
the blood. The blood in turn carries these foods in solution to 
the cells of the body and removes waste materials from them. 
It supplies tissues with oxygen and removes carbon dioxide. 
Heat produced by the oxidation of foods is carried by the blood 
from the internal organs to the surface of the body, where it is 
given off. Thus the blood regulates the temperature in dif- 
ferent parts of the body. 

In addition to these important uses the blood carries two kinds 
of substances of vital importance to the body, the hormones or 
regulative substances already spoken of, and the various anti- 
bodies or disease-resisting substances manufactured by the 
blood, as the agglu'tinins, precip'itins and hcemoly'sins. 

If we examine under the microscope a drop of blood taken 
from the frog or man, we find it made up of a fluid called 
plasma and two kinds of bodies, the so-called red corpuscles 
and colorless corpuscles, floating in this plasma. 

Composition of Plasma. — The plasma of human blood (when 
chemically examined) is found to be about 90 per cent water. 
It contains also amino-acids, some sugar, fat, and mineral 
material. It is, then, the medium which holds the fluid 
food that has been absorbed from within the intestine. When 
the blood returns from the tissues where the food is oxi- 
dized, the plasma brings back with it to the lungs most of 
the carbon dioxide liberated when oxidation took place. Blood 
returning from the tissues of the body has from 45 to 50 c.c 

§58 



COMPOSITION OF THE BLOOD 



359 



of carbon dioxide to every 100 c.c. (See Chapter XXVII.) 
Fibrin' ogen and some waste products to be spoken of later, 
are also found in the plasma. It also contains the hormones 
and the antibodies. 

Suggested Experiment : Clotting of Blood. — If fresh beef blood is al- 
lowed to stand over night, it will be found to have separated into two parts, 
a dark red, almost solid clot and a thin, straw-colored liquid called serum. 
Serum is made up of about 90 per cent water, 8 to 9 per cent protein, and 
from 1 to 2 per cent sugars, fats, and mineral matter. In these respects it 
very closely resembles the fluid food that is absorbed from the intestines. 

If another jar of fresh beef blood is poured into a pan and briskly 
whipped with a bundle of little rods (or with an egg beater), a stringy 
substance will be found to stick to the rods. This, if washed carefully, is 
seen to be almost colorless. Tested with nitric acid and amimonia, it is 
found to contain a protein substance called fibrin. 

Blood plasma, then, is made up of serum, a colorless fluid, 
and fibrinogen, or the fibrin in a fluid state. Under abnormal 
conditions, such as removal from the blood vessels, a compH- 
cated series of changes is started which ends with the formation 
of the tiny threads of fibrin in the blood, and the subsequent 
formation of a clot. A clot is simply a mass of fibrin threads 
with a large number of corpuscles tangled within. The clotting 
of blood is of great physiological importance, as it checks the 
flow of blood; otherwise we might bleed to death from the 
smallest wound. 

In blood within the circulatory system of the body, the fibrin 
is in the fluid form called fibrinogen. 
An enzyme, acting upon this fibrin- 
ogen under certain conditions, causes 
it to change to an insoluble form, 
the fibrin of the clot. 

The Red Blood Corpuscle; its 
Structure and Functions. — The red 
corpuscle in the blood of the frog is 
a true cell of disk-like form. The 
red corpuscle of man, however, lacks 
a nucleus. Its form is that of a biconcave disk. So small and 
so numerous are these corpuscles that over five million are found 
in a drop of normal blood. 




Human blood, highly magnified. 



360 



THE BLOOD AND ITS CIRCULATION 



The color, which is found to be a dirty yellow when separate 
corpuscles are viewed under the microscope, is due to a protein 
material called hmrnoglo'bin. Haemoglobin contains a large 
amount of iron. It has the power of uniting very readily with 
oxygen whenever that gas is abundant, and of giving it up 
to the surrounding media when oxygen is present in smaller 
amounts than in the corpuscle. This carrying of oxygen is the 
most important function of the red corpuscle, although the red 
corpuscle removes part of the carbon dioxide also from the 
tissues on its return to the lungs. The taking up of oxygen is 
accompanied by a change in color of the mass of corpuscles 
from a dull red to a bright scarlet. The red corpuscles arise 
as small cells in the red marrow of the living bones but soon 

lose their nuclei and are 
passed into the blood 
stream. After they are 
worn out it is believed 
»T7 that they are destroyed in 
the spleen and liver. 

The Colorless Corpuscle; 
Structure and Functions. 
— A colorless corpuscle is 

Colorless corpuscles v in the tissues outside ^ ^^^^ irregular in Outline, 
the blood vessels. A, small artery; C, capil- the shape of which is COn- 
laries; V, small vein. Highly magnified. j. j.i x^ • rpiu 

stantly changmg. these 
corpuscles are somewhat larger than the red corpuscles, but less 
numerous, there being about one colorless corpuscle to every 
seven hundred red ones. The colorless corpuscles have the power 
of movement, and can work their way between the cells in the 
walls of the blood vessels and wander into the tissues outside. 
There appear to be several varieties of colorless corpuscles; some 
are made in the lymph glands and others in the red marrow 
of bone. Their ultimate fate is uncertain, except in the case 
described in the next paragraph. 

A Russian zoologist, Metschnikoff, after studying a number 
of simple animals, such as medusse and sponges, found that in 
such animals some of the cells lining the inside of the food 
cavity take up or ingulf minute bits of food just as amoebae do. 




COMPOSITION OF THE BLOOD 



361 



Later, this food is changed into the protoplasm of the cell. 
Metschnikoff beheved that the colorless corpuscles of, the blood 
have somewhat the same function, and he later proved this to 
be true. Like the cells in the simple animals, the colorless 
corpuscles feed by ingulfing their prey. This fact has a 
very important bearing on the relation of colorless corpuscles 
to certain diseases caused by bacteria within the body. If, 
for example, a cut becomes infected by bacteria, inflammation 
may set in. Colorless corpuscles at once surround the spot 
and attack the bacteria. It has been 
found, however, that bacteria are not 
"' eaten " until they" are first bathed 
with a chemical substance known as an 
op'sonin. The presence of these op- 
sonins in the blood makes the bacte- 
ria attractive. If the bacteria are few 
in number, they are quickly destroyed 
by the colorless corpuscles, which are 
known as phag'ocytes. If bacteria are 
present in great quantities, they may 
prevail and kill the phagoc3^tes by 
poisoning them. The dead bodies of 
the phagocytes thus killed are found 
in the pus which accumulates in in- 
fected wounds. In case of a possible 
infection we must come to the aid of A colorless corpuscle A ingulf- 
the colorless corpuscles by washing the ^^^ germs . 

wound with some suitable antiseptic, as hydrogen peroxide. 
The Disease-resisting Mechanism of the Blood. — It is 
common knowledge that some of us ^' take " catching or in- 
fectious diseases more easily than others. Some fortunate 
people are immune to certain diseases or do not take them at 
all. Such immunity is brought about by the blood when a cer- 
tain substance is present in it and attacks and destroys bacteria 
by chemical action or by the work of the colorless corpuscles. 
This is an extremely complicated process which is probably 
caused by different substances which act specifically upon differ- 
ent kinds of bacteria. Just as each disease is caused by a 

HUNT. NEW ES. — 24 




362 THE BLOOD AND ITS CIRCULATION 

specific kind of germ, producing a specific kind of poison, so 
the blood appears to produce specific antibodies to fight these 
specific germs. 

The Amount of Blood and its Distribution. — Blood forms, 
by weight, about one thirteenth of the human bod}-. Its dis- 
tribution varies somewhat according to the position assumed by 
the bod}^ and the amount of undigested food in the stomach 
and intestines. Normally, about one half of the blood of the 
body is found in or near the organs l3'ing in the body cavity, 
about one fourth in the muscles, and the rest in the heart, lungs, 
large arteries, and veins. 

Blood Temperature. — The temperatm'e of blood in the human 
body is normall}^ about 98.5° Fahrenheit, although the temper- 
ature drops almost two degrees after we have gone to sleep at 
night. It is highest about 5 p.m. and lowest about 4 a.m. In 
fevers, the temperature of the bod}^ sometimes rises to 107° or 
higher; but unless this temperature is soon reduced, death fol- 
lows. Any considerable drop in temperature below the normal 
also would mean death. Body heat, as we know, results from 
the oxidation of food; the constant circulation of blood keeps 
the temperature nearly uniform in all parts of the body. The 
bod}^ temperature may be from two to three degrees higher im- 
mediately after violent exercise. Wh}-? 

Cold-blooded Animals. — In animals which are called cold- 
blooded, the blood has no fixed temperature, but varies with the 
temperature of the medium in which the animals live. Frogs, 
in the summer, may sit for hours in water with a temperature 
of almost 100°. In winter, they often endure freezing so that 
the blood and hnnph within the spaces under the loose skin are 
frozen into ice crystals. Such frogs, if thawed out carefully, 
will live. This change in bod}^ temperature is evidently an 
adaptation to the mode of life. 

Circulation of the Blood in Man. — The blood is the carrying 
agent of the body, and conveys materials from one part of the 
human organism to another. This it does by means of the 
organs of circulation — the heart and the blood vessels. The 
blood vessels include arteries which carry blood away from the 
heaxt, veins which bring blood back to the heart, and capillaries 



THE HEART 



363 




which connect the arteries with the veins. The organs of circu- 
lation thus form a system of connected tubes through which 
the blood flows in a continuous stream. 

The Heart; Position, Size, Protection. — The heart is a 
cone-shaped muscular organ about the size of the fist. It is 
located immediately above the diaphragm, and hes so that the 
muscular apex which points down- 
ward, moves while beating against the 
fifth and sixth ribs, just a little to the 
left of the midhne of the body. This 
fact gives rise to the notion that the 
heart is on the left side of the body. 
The heart is surrounded by a loose 
membranous bag called the pericar- 
dium, the inner lining of which secretes 
a fluid which surrounds the heart. 
When, for any reason, the pericardial 
fluid is not secreted, inflammation 
arises in that region. Do you know 

why? Diagram showing the front 

T 2. 10X X £ ja. -rr ± ^3,lf of the heart cut away: 

Internal Structure of the Heart.— ^^ ^orta; l, pulmonary ar- 

If we should cut open the heart of a terfes; la, left auricle; Iv, left 

mammal down the midhne, we could open?' n.' Wcus^d'Tr'^ mHml 
divide it into a right and a left side, valve closed; p and r, puimo- 
and show that each side has no internal ^^'rigirventrideTt! Tvet^ 

connection with the other. Each side cavae. Arrows show direction 
J /. ,1 . n -I ,. ..1 of circulation. 

IS made up oi a tmn-wailed portion with 

a rather large internal cavity, the auricle, and a smaller chamber 
with heavy muscular walls, called the ventricle. The auricles 
occupy the base of the cone-shaped heart; the ventricles, the 
apex. Communication between auricles and ventricles is regu- 
lated by little flaps of muscle called valves. The auricles receive 
blood from the veins and pass it on to the ventricles. The 
ventricles pump the blood into the arteries. From the left ven- 
tricle out through the aor'ta blood passes to all parts of the 
body. From the right ventricle the puVmonary arteries carry 
blood to the lungs. The openings to the arteries are guarded 
by three haK-moon-shaped flaps, which open so as to allow 



364 



THE BLOOD AND ITS CIRCULATION 



blood to pass away from the ventricle, and close to prevent 
itG going back when the muscles relax. 

The Heart in Action. — The heart is constructed on the same 
plan as a force pump, the valves preventing the rehux of 
blood into the auricles after it is forced out of the ventricles. 
Blood enters the auricles from the veins because the muscles 
of that part of the heart relax; this allows the space within 
the auricles to fill. Almost immediately the muscles of the 

ventricles relax, thus 
allowing blood to pass 
into the chambers 
within the ventricles. 
Then, after a short 
pause, during which 
time the muscles of the 
heart are resting, a 
wave of muscular con- 
traction begins in the 
auricles and ends in 
the ventricles, with a 
sudden strong contrac- 
tion which forces the 
blood out into the ar- 
teries. Blood is kept 
from flowing b a c k- 
wards by the valves, 
and is thus forced to pass into the arteries upon the contrac- 
tion of ventricle walls. 

The Course of the Blood in the Body. — Although the two 
sides of the heart are separate and distinct from each other, 
yet every drop of blood that passes through the right heart soon 
passes also through the left heart. There are two distinct 
systems of circulation in the body. The 'pulmonary circulation 
takes the blood through the right auricle and right ventricle, 
to the lungs, and passes it back to the left auricle. This is 
a relatively short circulation, in which the blood receives oxy- 
gen in the lungs and gives up its carbon dioxide. The greater 
circulation is known a3 the system'i^ circulation; in this system 





The heart is a force pump; prove it from these 
diaorrams. 



CIRCULATION OF THE BLOOD 



365 



the blood leaves the left ventricle through the great dorsal 
aorta. A large part of the blood passes directly to the muscles; 
some of it goes to the nervous system, kidneys, skin, and other 
organs of the body. It gives up food and oxygen, and receives 
the waste products of oxidation while passing through the capil- 
laries, and then returns to the right auricle through two large 
vessels known as the verm cavce. 

It requires from twenty to Capimrm 

thirty seconds only for the 
blood to make the complete 
circulation from the ventricle 
back again to the starting 
point. This means that the 
entire volume of blood in the 
human body passes three or 
four thousand times a day 
through the various organs of 
the body. 

Portal Circulation. — Some of the 
blood, on its return to the heart, 
passes by an indirect path to the 
walls of the food tube, absorbs food, 
and goes to the liver. Here the veins 
which carry the blood (called the 
portal veins) break up into capil- 
laries around the cells of the liver. 
We have already learned that tlie 
Uver is a great storehouse of animal 
sugar called glycogen. This glycogen 
is a food that may be easily oxidized 
to release energy, and is stored for 
that purpose. The sugar that be- 
comes glycogen is carried to the liver 
directly from the walls of the stom- 
ach and intestine, where it has been 
absorbed from the food there con- 
tained. From the liver, blood passes 
directly to the right auricle. The portal circulation consists of three veins 
which carry blood from the stomach and intestine to the liver, and is the 
only part of the circulation where the blood passes through two sets of 
capillaries, before going to the heart — one set in the walls of the stomach 
and intestine, and the other in the liver. 




Capillaries 



Diagram of the circulation of blood in a 
mammal. 



366 



THE BLOOD AND ITS CIRCULATION 




Capillary circulation in the web of a 
frog's foot, as seen under the com- 
pound microscope. 



Problem. — A study of the circulation of the blood. (Labora- 
tory Manual, Prob. XLIX; Laboratory Problems, Probs. 201 
to 206.) 

Circulation in the Web of a Frog*s Foot. — If the web of 
the foot of a hve frog or the tail of a tadpole is examined under 

the compound microscope, a 
network of blood vessels will be 
seen. In some of these the cor- 
puscles are moving rapidly and 
in spurts; these are arteries. 
The arteries lead into a network 
of smaller vessels or capillaries 
hardly greater in diameter than 
the width of a single corpuscle. 
The capillaries unite into larger 
veins in which the blood moves 
regularl}^ This illustrates the 
condition in any tissue of man 
where the arteries break up into capillaries which unite to form 
veins. 

Structure of the Arteries. — A distinct difference in structure 
exists between the arteries and the veins in the human bod}^ 
The arteries, because of the greater strain received from the 
blood which is pumped from the heart, have thicker muscu- 
lar walls, and in addition are very elastic. 

Cause of the Pulse. — The pulse, which can easily be detected by press- 
ing the large artery in the wrist or the small one in front of and above the 
external ear, is caused by the gushing of blood through the arteries after 
each pulsation of the heart. As the large arteries pass away from the 
heart, and divide, the diameter of each artery becomes smaller. At the very 
end of their course, these arteries are so small as to be almost microscopic 
in size and are very niunerous. There are so many that if they were 
placed together, side by side, their united diameter would be much greater 
than the diameter of the large artery (aorta) which passes blood from the 
left side of the heart. This fact is of very great importance, for the force 
of the blood as it gushes through the arteries becomes very much less when 
it reaches the smaller vessels. This gushing movement is quite lost when 
the capillaries are reached, first, because there is so much more space for 
the blood to fill, and secondly, because there is considerable friction caused 
by the very tiny diameter of the capillaries. 



CIRCULATION OF THE BLOOD 



367 



Capillaries. — The capillaries form a network of minute 
tubes everywhere in the body, but especially near the surface 
and in the lungs. It is through their walls that the food and 
oxygen pass to the tissues, and carbon dioxide is given up to 
the plasma. They form the connection between arteries and 
veins that completes the system of circulation of blood in the body. 

Function and Structure of the Veins. — If the arteries are 
supply pipes which convey fluid food to the tissues, then the 




Artery 



Valves in a 
vein. Notice 
the thin walls 
of the vein. 




Cells of lining^ 
membrdne 



Muscle and - 
elastic tissue 

Cells of lining 
membrane 



Muscle and 
elastic tissue 



Cross section of artery and vein. 



veins may be likened to drain pipes which carry away waste 
material from the tissues. Very numerous in the extrem- 
ities and in the muscles and among other tissues of the 
body, they, like the branches of a tree, become larger as they 
unite with each othe;:* on their way back to the heart. 

If the wall of a vein is carefully examined, it will be found to 
be neither so thick nor so tough as an artery wall. When 
empty, a vein collapses; the wall of an artery holds its shape. 
If you hold your hand down for a little time and then examine 



368 THE BLOOD AND ITS CIRCULATION 

it, you win find that the veins, which are relatively much nearer 
the surface than are the arteries, appear to be very much 
knotted. This appearance is due to the presence of tiny valves 
within the veins. These valves open in the direction of the 
blood cm-rent, but would close if the direction of the blood 
flow should be reversed (as in case a deep cut severed a vein). 
As the pressure of blood is much less in the veins than in the 
arteries, the valves aid in keeping the flow of blood in the veins 
toward the heart. The higher pressure in the arteries and the 
suction in the veins (caused by the enlargement of the chest 
cavity in breathing) are the chief factors which cause a steady 
flow of blood through the veins in the body. 

Problem. To study some changes in the composition of the 
blood. (Laboratory Manital, Prob. L; Laboratory Problems ^ 
Prob. 197.) 

The Ductless Glands and their Secretions. — One of the 

greatest discoveries of modern physiology is that many groups 
of gland cells give off to the blood internal secretions that play 
extremely important parts in the Hfe of man. Such glands are 
the suprare'nal bodies located just above the kidneys, the thy'- 
roid and parathy'roid glands in the neck, certain cells of the 
reproductive organs, and probably various other glands such 
as the pancreas and hver. An example of the lack of some 
internal secretions is seen in cre'tinism, a kind of idiocy. 
Here it is found that the disease is caused by a lack of 
internal secretions from the thjroid gland. If extracts of 
sheep's thyroid are fed to children who show cretinism they 
soon recover their normal condition. The suprarenal glands 
throw into the blood substances which act as an emergency 
hormone and stimulate the body to increased activity when 
this is necessary. An abnormal condition of the suprare- 
nals brings about a disease known as Addison's disease. The 
gland cells of the reproductive organs give the characteristics 
to the body which mark the differences in voice, average 
height and weight, etc., between boys and girls. Our knowledge 
of the work of the ductless glands is just beginning and future 
study will doubtless answer many interesting questions. 



CHANGES IN COMPOSITION OF BLOOD 369 



Function of Lymph. — Different tissues and organs of the. 
body are traversed by a network of tubes which carry the 
blood. Inside these tubes is the blood, consisting of a fluid 
plasma, the colorless corpuscles, and the red corpuscles. Out- 
side the blood tubes, in spaces between the cells which form 
tissues, is found another fluid, which is in chemical composi- 
tion very much Uke plasma of the blood. This is the lymph. 
It is, in fact, fluid food in which some colorless amoeboid cor- 
puscles are found. Blood gives up its food material to the 
lymph by passing it through the walls of the capillaries. The 
lymph surrounds the tissue cells and suppHes them with food. 

Some of the colorless 



VESSEL- /j 

CORPUSCLES K 




corpuscles from the blood 
make their way out be- 
tween the cells forming 
the walls of the capilla- 
ries, and enter the lymph. 
Lymph, then, is practically 
blood plasma plus some 
colorless corpuscles. It acts 
as the medium of exchange 

between the blood proper Diagram showing the exchange between blood 

and the cells in the tissues ^^^ *^^ ^^^^^ °^ *^^ ^°^y- 

of the body. The food supply thus brought enables the ceUs of 
the body to grow, the fluid food being changed to the proto- 
plasm of the cells. By means of the oxygen passed over by 
the lymph, oxidation may take place within the cells. Lymph 
not only gives food to the cells of the body, but also takes away 
carbon dioxide and other waste materials, which are ultimately 
passed out of the body by means of the lungs, skin, and kidneys. 

Lymph Vessels. — The lymph is collected from the various tissues of 
the body by means of a number of very thin-walled tubes, which are at 
first very tiny, but after repeated connection with other tubes ultimately 
unite to form large ducts. These lymph ducts are provided, like the veins, 
with valves. The pressure of the blood within the blood vessels forces 
continually more plasma into the lymph; thus a slow current is maintained 
from the lymph spaces toward the veins. On its course the lymph passes 
through many collections of gland cells, the lymph glands. In these glands 
impurities appear to be removed and some of the colorless corpuscles made. 



370 



THE BLOOD AND ITS CIRCULATION 



The lymph ultimately passes into a large tube, the thorac'ic duct, which 
flows upward near the ventral side of the spinal column, and empties into 
the large subclavian vein in the left side of the neck. Another smaller 

lymph duct enters the right sub- 
clavian vein. 

The Lacteals. — We have abeady 
found that part of the digested food 
(chiefly carbohydrates, amino-acids, 
salts, and water) is absorbed directly 
into the blood through the walls of 
the vilU and carried to the liver. Fat, 
however, is passed into the spaces in 
the central part of the villi, and 
from there into other spaces between 
the tissues, known as the lacteals. 
The lacteals form the most direct 
course for the fats to reach the blood. 
The lacteals and l3Tnph vessels have 
in part the same course. It will be 
thus seen that lymph at different 
parts of its course would have a very 
different composition. 

The Nervous Control of the Heart 
and Blood Vessels. — Although the 
muscles of the heart contract and 
relax without our being able to stop 
them or force them to go faster, yet in cases of sudden fright, or after a 
sudden blow, the heart may stop beating for a short interval. This shows 
that the heart is under the control of the nervous sj^stem. Two sets of 
nerve fibers, both of which are connected with the central nervous system, 
pass to the heart. One set of fibers accelerates, the other slows or inhibits, 
the heartbeat. The arteries and veins are also under the control of the 
sympathetic nervous system. This allows a change in the diameter of 
the blood vessels. Thus, blushing is due to a sudden rush of blood to 
the surface of the body, caused by an expansion of the blood vessels in 
that region. The blood vessels of the body are always full of blood. This 
results from an automatic regulation of the diameter of the blood vessels by 
a part of the nervous system called the vasomo'tor nerves. These nerves 
act upon the muscles in the walls of the blood vessels. In this way, each 
vessel adapts itself to the amount of blood in it at a given time. After 
a hearty meal, a large supply of blood is needed in the walls of the stom- 
ach and intestines; therefore, the arteries going to this region are dilated 
so as to receive an extra supply. When the brain performs hard work, 
blood is supplied in the same manner to that region. Hence, one should 
oot study or do mental work immediately after a hearty meal, for blood 




The lymph vessels: the dark spots are 
lymph glands; lac, lacteals; re, thoracic 
duct. 



CHANGES IN COMPOSITION OF BLOOD 371 



will be drawn to the brain, leaving the digestive tract with an insufficient 
supply. Indigestion may follow 'as a result. 

Effect of Exercise on the Circulation. — It is a fact familiar 
to all that the heart beats more violently and more quickly 
when we are doing hard work than when we are resting. Count 
your own pulse when sitting 
quietly, and then again after 
some brisk exercise in the 
gymnasium. Exercise in 
moderation is of undoubted 
value, because it sends more 
blood to those parts of the 
body where increased oxida- 
tion is taking place as the 
result of the exercise. The 
best forms of exercise are those 
which give work to as many 
muscles as possible — walking, 
out-of-door sports, any exer- 
cise that is not violent. Exer- 
cise should not be attempted 
immediately after eating, as 
this causes a withdrawal of 

blood from the digestive glands ^ Stopping flow of blood frojn an artery 
, „ ,, ,, . ., by applying a tight bandage (hgature) 

and from the walls Ot the between the cut and the heart. 

food tube to the muscles of 

the body. Neither should exercise be continued after one is 
tired, as poisons are then formed in the muscles, which cause 
fatigue. Remember that hard v/ork given to the heart by 
extreme exercise may injure it, causing possible trouble with 
the valves. 

Treatment of Cuts and Bruises. — Blood which oozes slowly 
from a cut will usually be checked by the natural means of the 
formation of a clot. A cut or bruise should, however, be washed 
in a weak solution of carbolic acid or some other antiseptic 
and kept covered with clean gauze in order to prevent bacteria 
from obtaining a foothold on the exposed flesh. If blood, issuing 
from a wound, is bright red in color and gushes in distinct pulsa- 




372 



THE BLOOD AND ITS CIRCULATION 



tions, an artery has been severed. To prevent the flow of blood, 
a tight bandage must be bound on between the cut and the heart. 
A handkerchief tied with a knot placed over the artery may stop 
bleeding if the cut is on one of the limbs. If this does not 
serve, then insert a stick in the handkerchief and twist it so 
as to make the pressure around the limb still greater. Thus 
we may close the artery until the doctor arrives and he may 
sew up the injured blood vessel. If a vein is cut the blood flows 
out in a steady stream. When the loss of blood is great it may 
be checked by a tight bandage on the side of the cut, away from 
the heart. 

The Effect of Alcohol upon the Blood. — It has recently 
been discovered that alcohol has an extremely injurious effect 




A comparison of the chances of illness and death in drinkers and non-drinkers. 
For each age shown, the light shaded area represents the probability of sickness 
and death for drinkers, as compared with the dark area marked 100 for non- 
drinkers. For example, if among non-drinkers aged 15 to 24 years 100 out of 8,200 
are sick, then the diagram indicates that among drinkers of the same age probably 
180 out of 8,200 would be sick. 

upon the colorless corpuscles of the blood, lowering their 
ability to fight disease germs to a marked degree. This is 
clearly shown in a comparison of deaths from certain infectious dis- 
eases of drinkers and of abstainers, the percentage of mortality 
being much greater in the former. 



CHANGES IN COMPOSITION OF BLOOD 373 

The Effect of Alcohol on the Circulation. — Alcoholic drinks 
affect the very delicate adjustment of the nervous centers con- 
trolHng the blood vessels and heart. Even very dilute alcohol 
relaxes the muscles of the tiny blood vessels, consequently 
more blood is allowed to enter them, and, as the small vessels 
are usually near the surface of the body, the habitual redness 
seen in the face of hard drinkers is the ultimate result. The 
walls of the arteries become hardened and lose their elasticity 
when alcohol is in the system. 

Summary. — Blood is really liquid food containing two types 
of cells, red and colorless corpuscles. The former are oxygen 
carriers, the latter protect the body from disease. 

Blood is kept in circulation within arteries, capillaries, and 
veins, by a double force piunp called the heart. The fluid 
part of the blood with its load of food and gases, gets through 
the walls of the smallest blood vessels and bathes the individual 
cells of the body so that they may take up this food and 
oxygen passed in to them. They in turn give up wastes and 
carbon dioxide to the Ijrmph, as this fluid is called. 

Problem Questions. — 1. Is the blood a tissue? Why? 

2. What is the function of the red corpuscles? of colorless 
corpuscles ? 

3. What is the composition of plasma? How do you account 
for this? 

4. How does lymph dijffer from pla&ma? 

5. Prove that the heart is a force pimip. 

6. Compare the short and long circulations in the body. 

7. How do cells get food and get rid of wastes ? How . do 
they "breathe"? 

Problem and Project References 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 
Hunter and Whitman, Civic Science. American Book Company. 
Martin, Human Body (for hormones). Henry Holt and Company, 
Peabody, Studies in Physiology. The Macmillan Company. 
Sharpe, A Laboratory Manual. American Book Company. 
Stiles, Nutritional Physiology. W. B. Saunders Company, 



XXVII. RESPIRATION AND EXCRETION 



Problem. A study of the organs and the process of respiration 
to determine — 

(a) Organs of respiration in frog. 

(b) Mechanics of respiration. 

(c) Process of respiration m the lungs, 

{Laboratory Manual, Prob. LI; Laboratory Problems, Probs. 
207 to 213.) 

Necessity for Respiration. — We have seen that plants and 
animals need oxygen in order that the life processes may go on. 

Food is oxidized to release 
energy, just as coal is 
burned to give heat to 
run an engine. As a draft 
of air is required to make 
fire under the boiler, so, 
in the human body, oxy- 
gen must be given so 
that foods in the tissues 
may be oxidized to release 
energy used in growth. 
This oxidation takes place 
in the cells of the body, 

Air passages in the human lungs: a, larynx; be they part 01 a mUSCle, 
6, trachea (or windpipe) ; c, c^, bronchi; e, bron- q Poland Or the brain, 
chial tubes; /, cluster of air cells. ^ttt i ti 7 i'' 

The red blood corpuscles 
in their circulation to all parts of the body are the agents which 
convey oxygen to those places in the body where it will be used. 
Respiration is taking in oxygen and giving off carbon dioxide by 
the cells. 

The Organs of Respiration in Man. — We have alluded to 
the fact that the lungs are the organs which give oxygen to 
the blood and take from it carbon dioxide. The course of air 

374 




ORGANS AND MECHANICS OF RESPIRATION 375 



passing from the outside to the lungs in man is much the same 
as that in the frog. Air passes through the nostrils, the pharynx, 
the glottis, and into the windpipe. This cartilaginous tube, the 
top of which may easily be felt as the Adam's apple of the throat, 
divides into two bronchi (brong'ki) , each of which goes to a lung. 
The bronchi within the lungs break up into a great number of 
smaller bronchial tubes, which divide somewhat like the small 
branches of a tree, and end in air sacs. This branching in- 
creases the surface of the air 
tubes within the lungs. 
There are several adapta- 



Bronchial 
Tube 



Pulmonary 



Artery 



Pu/monary 




tions which should be noted 
at this point. The folds in 
the inside of the nose passage 
warm and moisten the air 
somewhat before it enters the 
bronchi. The hairs in the 
nose passage act as a strainer 
which keeps most of the dust 
and germs out from the lungs. 
Then the bronchial tubes, in- 
deed all the air passages, are 
lined with cilia, which are 
constantly in motion, beating 
with a quick stroke toward 
the mouth. Hence, if any for- 
eign material should get into 
the windpipe or bronchial tubes, it would be pushed upward by 
the action of the cilia. It is by means of cilia that phlegm is 
raised into the throat. Such action is of great importance, as 
it prevents the air passages from filling with foreign matter. 
The bronchial tubes end in very minute air sacs — little 
pouches having elastic walls — into which air is taken when 
we inspire or take a deep breath. In the walls of the air sacs 
are numerous capillaries. It is through the very thin walls of the 
air sacs that an interchange of gases takes place which results in 
the blood giving up carbon dioxide and taking up oxygen. 
The Pleura. — The lungs are covered with a thin elastic 



Diagram to show what the blood gains 
and loses in one of the air sacs of the 
lungs. 



376 



RESPIRATION AND EXCRETION 



membrane, the pleura, which forms a bag in which the lungs 
are hung. Between the walls of the bag and the lungs is a 

space filled with lymph. 
mribj^^^-^. By this means the lungs 
are prevented from rub- 
bing against the walls of 
the chest. 

Breathing. — In every 
full breath there are two 
distinct movements, in- 
spiration (taking air in) 
and expiration (forcing 
air out). In man an in- 
spiration is produced by 
the contraction of the 
muscles between the ribs 




^fiiaphragm 



Diagram showing portion of diaphragm and 
ribs in (a) expiration; (6) inspiration. 



together with the contraction of the diaphragm, the muscular 
wall forming the floor of the 
chest cavity; this results in 
pulling down the diaphragm 
and pulling upward and out- 
ward the ribs, thus making 
the space within the chest 
cavity larger. The lungs, 
which lie within this cavity, 
are filled by the air rushing 
into the larger space thus 
made. An expiration is simpler 
than an inspiration, for it re- 
quires no muscular effort; the 
muscles relax, the breastbone 
and ribs sink into place, while 
the diaphragm returns to its 
original position and the air is 
pushed out. 

Experiment to Illustrate the Me- 
chanics of Breathing. — A piece of apparatus which illustrates to a degree 
the mechanics of breathing may be made as follows: Attach a string to the 




Apparatus to show the mechanics of 
breathing. 



ORGANS AND MECHANICS OF RESPIRATION 377 

middle of a piece of sheet rubber. Tie the rubber over the large end of a 
bell jar. Pass a glass Y tube through a rubber stopper. Fasten two small 
toy balloons to the branches of the tube. Close the small end of the jar 
with the stopper. Adjust the tube so that the balloons shall hang free in 
the jar. If now the rubber sheet is pulled down by means of the string, the 
air pressure in the jar is reduced and the toy balloons within expand, owing 
to the air pressure down the tube. When the rubber is allowed to go back 
to its former position, the balloons collapse. 

Rate of Breathing and Amount of Air Breathed. — During 

quiet breathing, the rate of inspiration is from 
fifteen to eighteen times per minute; this rate 
depends largely on the amount of phj'-sical 
work performed. About 30 cubic inches of 
air are taken in and expelled during the 
ordinary quiet respiration. The air so 
breathed is called tidal air. In a '' long 
breath/' we take in about 100 cubic inches 
in addition to the tidal air. This is called 
complemental air. By means of a forced ex- 
piration, it is possible to expel from 75 to 
100 cubic inches more than tidal air; this 
air is called reserve air. What remains in the 
lungs, amounting to about 100 cubic inches, 
is called the residual air. The value of deep 
breathing is seen by a glance at the diagram. 
When we take a full breath we ventilate the 



WOCOJN, 



TIDAL AIR 
30CU.IN. 



wmm 



RESIDUAL 

AIR 
100 CU.IN. 



230 
CUM 



Amounts and pro- 
portions of comple- 

lung sacs which otherwise would not be mental, tidal, re- 

] jxu 1 J.11 rj-T- serve, and residual 

used, and thus we clear the lungs of the ^ir in the breathing 
reserve air with its accompanying load of of an average adult 

1 T • 1 ' man. 

carbon dioxide. 

Respiration under Nervous Control. — The muscular movements which 
cause an inspiration are partly under the control of the will, but the 
movement is not wholly under our control. The nerve centers which govern 
inspiration are part of the sj^mpathetic nervous system. Anything of an 
irritating nature in the trachea or larynx will cause a sudden expiration or 
cough. When a boy runs, the quickened respiration is due to the fact 
that oxygen is used up rapidly and a larger quantity of carbon dioxide is 
formed. This stimulates the nervous center which has control of respiration 
to greater activity, and quickened inspiration follows. 



HUNT. NEW ES. — 25 



378 RESPIRATION AND EXCRETION 

Problem. A study to determine the products of respiration. 
(Laboratory Manual, Prob. LI I.) 

Changes in Air in the Lungs. — Air is much warmer after 
leaving the lungs than before it enters them. Breathe on the 
bulb of a thermometer to prove this. Expired air contains a 
considerable amount of moisture, as may be proved by breath- 
ing on a cold pohshed surface. This it has taken up in the air 
sacs of the lungs. The presence of carbon dioxide in expired air 
may be detected easily by the limewater test. Air such as we 
breathe out of doors contains, by volume : — 

Oxygen 20.96 

Carbon dioxide 04 

Nitrogen (and other gases) , 79 

Air expired from the limgs contains : — 

Oxygen 16.02 

Carbon dioxide 4.38 

Water vapor .60 

Nitrogen (and other gases) 79 

In other words, there is a loss of between four and five per 
cent oxygen, and nearly a corresponding gain in carbon dioxide, 
in expired air. There are also some other organic substances 
expeUed. The volume of carbon dioxide given off is always a 
little less than the volimae of oxygen taken in. This seems to 
show that some oxygen unites with some of the chemical ele- 
ments in the body. 

Changes in the Blood within the Lungs. — Blood, when leav- 
ing the lungs, is much brighter red than when entering them. 
The change in color is due to an absorption of oxygen by the 
hcemoglobin of the red corpuscle. The changes taking place in 
the blood are obviously the reverse of those that take place in 
the air in the limgs. Blood in the capillaries within the lungs 
gains from four to five per cent of oxygen which the air loses. At 
the some time blood loses the four per cent of carbon dioxide which 
the air gains. The blood, while in the lungs, gives off water 
vapor also, amounting to nearly one half a pint of water 
daily. 



VENTILATION 



379 




o\ 



' ^^v{^?! villi 



Problem. A study of ventilation. (Laboratory Manual, Prob. 
LIII; Laboratory Problems, Probs. 214 to 218.) 

Need of Ventilation. — Air in a living room or a schoolroom con 
tains, besides dust and bacteria, carbon dioxide and other wastes 
given off from the human body. About 0.6 of a cubic foot 
of CO2 is given off from the body 
every hour. In addition to this a 
large amount of moisture is given 
to the atmosphere of a crowded 
room and heat is dissipated from our 
bodies. We all know the discomfort 
felt in a crowded room with win- 
dows and doors closed. In order 
that the air bearing this heat, 
humidity, and carbon dioxide be 
removed and fresh air substituted 
it is necessary for us to ventilate 
our buildings. 

How We Ventilate. — In our 
homes, ventilation is usually ac- 
complished by opening windows. A 
glance at the diagram shows three 
methods of ventilation. Which is 
the most adequate, and why? Too 
often people think they ventilate by 
opening a window either at the top 
or bottom only. This changes the 
air in only a very small part of the for air. Which is the best method 

1 « T 1 of ventilation? Explain. 

room, h ortunately for us the cracks 

under and around doors, windows, and baseboards, and fire- 
places give us much natural ventilation. (See the diagram.) 
Two thousand to three thousand cubic feet of air per hour is 
usually considered the average need of fresh air for each person. 
In schoolhouses or other public buildings, where many are in one 
room for a considerable period of time, it becomes necessary to 
have artificial methods of ventilation. This is usually accom- 
plished by means of pumping warm air through ducts into a 




Three ways of ventilating a 
room: i, inlet for air; o, outlet 



380 



RESPIRATION AND EXCRETION 



room and sucking the stale air out through similar ducts. In 
some instances the air is passed through a filter or is washed 
to remove impurities. Often it passes in near the floor, some- 
times from above. Describe the system used in your school 
and see if you can understand the science underlying its 
plan. 

Sweeping and Dusting. — It is very easy to demonstrate the 
amount of dust in the air by looking at a beam of light in a 
darkened room. We have already proved that spores of mold 

and yeast exist in the air. 
That bacteria are also 
present may be proved 
by exposing a sterilized 
gelatin plate to the aii 
in a schoolroom for a few 
moments.^ 

Many of the bacteria 
present in the air are 
active in causing diseases 
of the throat and lungs, 
such as diphtheria, mem- 
branous croup, tubercu- 
losis, colds, bronchitis 
(inflammation of the 
bronchial tubes), and 
pneumonia (inflamma- 




Plate culture exposed for five minutes in a 
school hall where pupils were passing to recita- 
tions. Each spot is a colony of bacteria or mold. 



tion of the tiny air sacs of the lungs). 

Dust, with its load of bacteria, will settle on any horizontal 
surface in a room not used for three or four hours. When a 
vacuum cleaner is not available dusting and sweeping should 
always be done with cloth and broom which are damp, other- 
wise the bacteria are simply stirred up, sent into the air, and 
allowed to settle down on the furniture and floor again. The 
proper watering of streets before they are swept is also an im- 
portant factor in preserving health. 

^ Expose two sterilized dishes containing culture media ; one in a room being 
swept with a damp broom, and the other in a room which is being swept in 
the usual manner. Note the formation of colonies of bacteria in each dish. 
In which dish does the greater number of colonies form? Why? 



VENTILATION 381 

Ventilation of Sleeping Rooms. — Sleeping in close rooms is 
the cause of much illness. Beds should be placed so that a 
constant supply of fresh air is obtained without a direct draft. 
This may often be managed with the use of screens. Bedroom 
windows should be thrown open in the morning to allow free 
entrance of the sun and air, bedclothes should be washed fre- 
quently, and sheets and pillow covers often changed. Bedroom 
furniture should be simple, and but little drapery allowed in 
the room. 

Hygienic Habits of Breathing. — Every one should form the 
habit of inspiring slowly and deeply and to the full capacity of 
the lungs upon going into the open air. A slow expiration 
should follow, forcing out as much air as possible. Breathe 
through the nose, thus warming the inspired air before it 
enters the lungs and chills the blood. Repeat this exercise 
several times every day. You will thus prevent certain of the 
air sacs which are not often used from becoming hardened and 
permanently closed. 

The Relation of Tight Clothing to Correct Breathing. — It 
is impossible to breathe correctly unless the clothing is loose 
over the chest and abdomen. Tight corsets and tight belts pre- 
vent the walls of the chest and the abdomen from pushing out- 
ward and interfere with the drawing of air into the lungs. They 
may also result in permanent distortion of parts of the skeleton 
directly under the pressure. Other organs of the body cavity, 
as the stomach and intestines, may be forced downward, out of 
place, and in consequence they do not perform their work 
properly. r 

Relation of Exercise to Deep Breathing. — We have already 
seen that exercise results in the need of greater food supply, 
and hence a more rapid pumping of blood from the heart. 
With this comes need of more oxygen to allow oxidation which 
supplies the greater energy used. Hence deeper breathing dur- 
ing time of exercise is a prime necessity in order to increase the 
absorbing surface of the lungs. 

Suffocation and -Artificial Respiration. — Suffocation results 
from the shutting off of the supply of oxygen from the lungs. It 
may be brought about by an obstruction in the windpipe, by a 



382 



RESPIRATION AND EXCRETION 



lack of oxygen in the air, by inhaling some other gas in quantity, 
or b}^ drowning. A severe electric shock may paralyze the ner- 
vous centers which control respiration, thus causing a kind of 
suffocation. In the above cases, death often may be prevented 
by prompt recourse to artificial respiration. To accomplish this, 
lay the person face down, with the forehead resting on one 

arm. This position will 
bring the tongue forward 
and allow the water to es- 
cape from the lungs if it is 
a case of drowning. Now 
get astride of the patient, 
with one hand on each side 
of the body, place the 
fingers on the ribs and 
press down and in. Relax 
the pressure so as to allow 
air to get into the lungs. 
Repeat this about fifteen 
times a minute and con- 
tinue if necessary for three 
or four hours. 

Common Diseases of the 
Nose and Throat. — Catarrh is^ a disease to which people with 
sensitive mucous membrane of the nose and throat are subject. 
It is indicated by the constant secretion of mucus from this 
membrane. Frequent spraying of the nose and throat with 
some mild antiseptic solution is found useful. Chronic catarrh 
should be attended to by a physician. Often we find children 
breathing entirely through the mouth because the air passages in 
the nose are closed. When this goes on for some time the nose 
and throat should be examined by a physician for enlarged tonsils 
and adenoids, or growths of soft masses of tissue which fill up 
the nose cavity, thus causing mouth breathing. Many a child, 
backward at school, thin and irritable, has been changed to a 
healthy, normal, bright pupil by the removal of adenoids. 
Sometimes the tonsils at the back of the mouth cavity become 
diseased as well as enlarged, and are the cause of colds and tliroat 




Schaefer method of artificial respiration. 



ORGANS OF EXCRETION 



383 



troubles as well as the beginning of tuberculosis. Infected 
tonsils sometimes cause acute rheumatism and heart trouble. 

Cell Respiration. — It has been found, in the case of very 
simple animals, such as the amoeba, that when oxidation takes 
place in a cell, work results 



from this oxidation. The oxy- 
gen taken into the lungs is not 
used there, but is carried by 
the blood to such parts of the 
body as need oxygen to oxidize 
food materials in the cells. 
The quantity of oxygen used 
by the body is nearly depend- 
ent on the amount of work 
performed. From twenty to 




l/mphrube 0- •- 



The respiration of a cell. 



twenty-five ounces of oxygen is taken in and used by the body 
every day. Oxygen is constantly taken from the blood by tissues 
in a state of rest and is used up when the body is at work. 

While work is being done certain wastes are formed in the cell. 
Carbon dioxide is released when carbon is burned; and when 
proteins are burned, a waste product containing nitrogen is 
formed. These wastes must be passed off from the cells, as they 
are poisons. Here again the blood and lymph, common carriers, 
take the waste materials to places where they may be excreted 
or passed out of the body. 

Organs of Excretion. — ■ All the life processes which take place 
in a living thing result ultimately, in addition to giving off car- 
bon dioxide, in the formation of organic wastes which contain 
nitrogen. In animals one of these wastes is called u'rea. In 
man, the lungs, skin, and kidneys perform the function of 
eliminating wastes and are called the organs of excretion. 

The Human Kidney. — The human kidney is about four inches 
long, two and one half inches wide, and one inch thick. Its 
color is dark red. If the structure of the medulla and cortex 
of the kidney (Figure, p. 384) is examined under the compound 
microscope, you will find these regions to be composed of a vast 
number of tiny branched and twisted tubules. The outer end of 
each of these tubules opens into the 'pelvis, the space within the 



384 



RESPIRATION AND EXCRETION 



kidney; the inner end forms a tiny closed sac in the cortex. 
In each sac, the outer wall of the tube has grown inward and 
carried with it a very tiny artery which breaks up into a mass 

of capillaries. These capil- 




Cortex 

Medulla 

■Pyrdmids 

Pelvis 
Ureter 



Lengthwise section of kidney. 



laries, in turn, unite to form a 
small vein as they leave the 
little sac. Each of these sacs 
with its wall netted with blood 
vessels is called a glomer'ulus. 
Wastes given off by the 

'A~D lA t- ^^^^^ i^ the Kidney. — In the 
ll ^ glomerulus the blood loses by 

osmosis, through the very thin 
walls of the capillaries, first, a 
considerable amount of water 
(amounting to nearly three 
pints daily); second, a nitrog- 



enous waste material known as urea; third, salts and other 
waste organic substances, uric acid among them. 

These waste products, together with the water containing them, are 
known as urine. The total amount of 
nitrogenous waste leaving the body each 
day is about twenty grams; this is nearly 
all accounted for in the urea passed off by 
the kidney. The urine is passed through 
the ureter (u-re'ter) to the urinary bladder; 
from this reservoir it is passed out of the 
body, through a tube called the ure'thra. 
After the blood has gone through the 
glomeruh of the kidneys it is purer than 
in any other place in the body, because, 
before going there, it lost a large part of 

its carbon dioxide in the lungs, and in the ra, small renal artery; GL, capil- 
kidneys it lost much of its nitrogenous laries in the glomerulus; RVy 
waste. So dependent is the body upon small renal vein ; C tubule lead- 
., , . c -. • J. • 1 xu X iiig to the pelvis of the kidney, 

the excretion of its poisonous material that, 

in cases where the kidneys do not do their work properly, death may ensue 
within a few hours. 




A glomerulus, much magnified: 



Structure and Use of Sweat Glands. — If you examine the 
surface of your skin with a lens, you will notice the surface is 



ORGANS OF EXCRETION 385 

thrown into little ridges (see diagram, page 313). Between the 
ridges may be found a large nimiber of very tiny pits; these are 
the pores or openings of the sweat-secreting glands. From each 
opening a little tube penetrates deep within the dermis; there, 
coiling around upon itseK several times, it forms the sweat 
gland. Close around this coiled tube are found many capillaries. 
From the blood in these capillaries, cells lining the wall of the 
gland take water, and with it a little carbon dioxide, urea, and 
some salts (common salt among others). This forms the excre- 
tion known as sweat. The combined secretions from these glands 
amount normally to a little over a pint during twenty-four hours. 
At all times, a small amount of sweat is given off, which is 
evaporated or is absorbed by the underwear; as this passes off 
unnoticed it is called insensible perspiration. In hot weather or 
after hard manual labor the amount of perspiration is greatly 
increased. 

Relation of Body Heat to Work Performed. — The body 
temperature of a person engaged in manual labor will be found 
to be but Httle higher than the temperature of the same person 
at rest. When a man works, he releases energy by oxidizing 
food material or tissue in the body and heat is released. Mus- 
cles, nearly one half the weight of the body, release about five 
sixths of their energy as heat. At aU times they are giving up 
some heat. How is it that the body temperature is not much 
higher when work is being done than when at rest? 

Regulation of Heat of the Body. — The temperature of the 
body is largety regulated by means of the activity of the sweat 
glands. The blood carries much of the heat, liberated in the 
various parts of the body by the oxidation of food, to the sur- 
face of the body, where it is lost in the evaporation of sweat. 
In hot weather the blood vessels of the skin are dilated; in cold 
weather they are made smaller by the action of the nervous 
system. The blood loses water in the skin, and as the water 
evaporates, we are cooled off. The object of increased perspira- 
tion, then, is to remove heat from the body. With a large amount of 
blood present in the skin, perspiration is increased; with a 
small amount, it is diminished. Hence, we have in the skin a 
regulator of body temperature under automatic control. 



386 RESPIRATION AND EXCRETION 

Sweat Glands under Nervous Control. — The sweat glands, like the 
other glands of the body, are under the control of the sympathetic nervous 
system. Frequently the nerves dilate the blood vessels of the skin, thus 
helping the sweat glands to secrete, by giving them more blood. 

" Thus regulation is carried out by the nervous system determining, on 
the one hand, the loss by governing the supply of blood to the skin and the 
action of the sweat glands; and on the other, the production by dimin- 
ishing or increasing the oxidation of the tissues." — Foster and Shore, 
Physiology. 

Comparison with Cold-blooded Animals. — We have seen that the body 
temperature of a frog remains nearly the same as that of the surrounding 
medium. Fishes, aU amphibious animals, and reptiles are alike in this re- 
spect. This change in the body temperature is due to the absence of regu- 
lation by the nervous system. A sort of regulation is exerted, however, by 
outside forces, for the cold in winter causes the cold-blooded animals to 
become inactive. Warm weather, on the other hand, stimulates them to 
greater activity and to increased oxidation. This is naturally followed by 
an increase in body temperature. 

Problem. A final study of changes in the composition of blood 
in various parts of the body. (Laboratory Manual, Prob. LIV; 
Laboratory Problems, Prob. 219.) 

Summary of Changes in Blood within the Body. — We have al- 
ready seen that red corpuscles in the lungs lose part of their load 
of carbon dioxide that they have taken from the tissues, replac- 
ing it with oxygen. This is accompanied by a change of color 
from a deep crimson (in blood which is poor in oxygen) to that of 
bright scarlet (in richly oxygenated blood). More changes take 
place in other parts of the body. In the walls of the food tube, 
especially in the small intestine, the blood receives its load of 
fluid food. In various parts of the body it receives enzymes 
and hormones. In the muscles and other working tissues the 
blood gives up food and oxygen, receiving carbon dioxide and 
organic waste in return. In the liver, the blood gives up its 
sugar, and the worn-out red corpuscles which break down are 
removed (as they are in the spleen) from the circulation. In 
glands, it gives up materials used by the gland cells in their 
manufacture of secretions. In the kidneys, it loses water and 
nitrogenous wastes (urea). In the skin, it also loses some waste 
materials, salts, and water. 

Hygiene of the Skin. — The skin as an organ of excretion is 



COLDS AND FEVERS 387 

of importance. It is of even greater importance as a regulator 
of body temperature. The mouths of the sweat glands must 
not be allowed to become clogged with dirt. The skin of the 
entire body should, if possible, be bathed daily. For those who 
can stand it, a cold shower or sponge bath in the morning is 
best. Soap should be used daily on parts exposed to dirt. 
Exercise in the open air is important to all who desire a good 
complexion. 

Cuts and Burns. — In case the skin is broken the entrance 
and growth of bacteria may be prevented by applying iodine 
or by washing the wound with weak antiseptic solutions, such 
as 3 per cent carbolic acid, 3 per cent lysol (li'sol), peroxide of 
hydrogen (full strength), or a xV per cent solution of hichlo'ride 
of mercury. These solutions should be applied immediately. 
In the case of a burn apply a mixture of equal parts of linseed 
oil and lime water, or if this is not at hand cover the injured 
part with a paste of baking soda and water. In the case of a 
bad burn or deep cut call a doctor at once. 

Colds and Fevers. — The regulation of blood passing through 
the blood vessels is under control of the nervous system. If 
this mechanism is interfered with in any way, the sweat glands 
may not do their work, perspiration may be stopped, and the 
heat from oxidation held within the body. The body tempera- 
ture goes up, and a fever results. 

If the blood vessels in the skin are suddenly cooled they 
contract and send the blood elsewhere. If the chiUing of the 
blood is too great or lasts for too long a time, a congestion or 
cold foUows. Colds are, in reality, a congestion of membranes 
lining certain parts of the body, as the nose, throat, windpipe, 
or lungs, and a growth of bacteria which were present in the 
mouth or throat. Some colds are contagious and gain entrance 
to the body when the resistance is low. 

When suffering from a cold, it is therefore important not to chill 
the skin, as a full blood supply should be kept in it and away 
from the seat of congestion. For this reason hot baths (which 
call the blood to the skin), the avoiding of drafts (which chill the 
skin), and warm clothing are useful factors in the care of colds. 

One of the greatest deceptions played upon the drinker by 



388 



RESPIRATION AND EXCRETION 




alcohol is that it helps to make him warmer when he is cold. 
But this is far from the case. As a matter of fact he feels 
warmer for a little while because the alcohol paralyzes the nerves 
which control the amount of blood going to the skin and the 
skin becomes flushed and gorged with blood. But as we have 

seen under such conditions heat 
is lost from the blood through 
the skin. In a short time 
therefore the drinker has lost 
more heat than the abstainer 
and numerous cases are on 
record where drinkers have 
suffered or lost their lives from 
exposure while abstainers un- 
der the same conditions have 
survived. 
Alcohol and tobacco have 

^W5b.?-=^^So^oO^^J'^S^ bad effect upon respiration and 

the cells Hning the respiratory 
organs. Statistics show with- 
out a doubt that the use of 
alcohol together with bad con- 
ditions of living has had a 
very serious effect in raising 
the death rate from tubercu- 

At blood vessels in skin normal; B, when ]osis of the lunes 
congested. a i i i i i* 

Alcohol also has a serious 
effect upon the kidneys. It is well known to alcoholic drinkers 
that even beer and light wine are prohibited to the man who 
has kidney trouble. Moreover, much of the fatty degeneration 
of the kidneys, and Bright's disease may be attributed directly 
to the overuse of alcohol. 

Summary. — Respiration really takes place in the cells of the 
body where work is done. The structures which provide for 
this are the lungs and blood vessels, which allow the air taken 
in to come in contact with the blood through the delicate linings 
of the lung sacs. 







B 



RESPIRATION AND EXCRETION 389 

Since oxidation takes place in cells the products of burning 
must be removed as well as other organic wastes. This is 
done eventually by the lungs, skin, and kidneys. 

Problem Questions. — 1. How are the lungs adapted to their 
work? 

2. Explain the mechanics of breathing. 

3. What are the products of respiration? 

4. What is ventilation? Why is it necessary? 

5. What is cell respiration? Explain fully. 

6. How does the kidney do its work? 

7. How does the skin excrpte wastes? j 

8. What is a congestion and how is it caused? 

Problem and Project References 

Eddy, General Physiologij. American Book Company. 

Fisher and Fisk, How to Live. Funk and Wagnalls Company. 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Hunter and Whitman, Civic Science. American Book Company. 

Martin, The Human Body. Henry Holt and Company. 

Sharps, A Laboratory Manual. American Book Company. 




■Cell Body 
"Nucleus 



XXVIII. THE NERVOUS SYSTEM AND ORGANS 

OF SENSE 

Problem. A study of the nervous system, reactions to stimuli, 
and habit formation. (Laboratory Manual, Prob. L V ; Laboratory 
Problems, Probs. 220 to 233.) 

Divisions of the Nervous System. — In a complicated machine 
like the human body there must be some means of obtaining 

cooperative action of 
the different organs to- 
ward definite ends. In' 
the vertebrate animals, 
such as man, this is 
brought about by two 
divisions of the nervous 
system. One includes 
the brain, spinal cord, 
and cranial and spinal 
nerves, which together 
make up the cerebro- 
spinal nervous system. 
The other division is 
called the autonom'ic or 
sympathetic nervous sys- 

The central cerebro-spinal tem. The activities of Diagram of a neuron 
nervous system. ^^^ ^^^^ ^^^ Controlled or nerve unit. 

from nerve centers by means of fibers which extend to all parts 
of the body, and end in muscles. The brain and spinal cord are 
examples of such centers, since they are largely made up of 
nerve cells. Small collections of nerve cells, called ganglia, are 
found in other parts of the body. These nerve centers are con- 
nected, to a greater or less degree, with the surface of the body 
by the nerves which serve as pathways between the end organs 

890 








Axis Cylinder 



Ner/eEnds 



BRAIN AND NERVES 391 

of touch, sight, taste, etc., and the centers in the brain or spinal 
cord. Thus sensation is obtained. 

Nerve Cells and Fibers. — A nerve cell, like other cells in the 
body, is a mass of protoplasm containing a nucleus, but, un- 
like them, it is usually rather irregular in shape, and possesses 
many delicate, branched protoplasmic projections. One of these, 
the axis cylinder, is much longer than the others and forms the 
pathway over which nervous impulses travel to and from the 
nerve centers. A nerve cell is ■ a center of activity and sends 
impulses over this thin strand of protoplasm (the axis cylinder 
process) prolonged into a nerve fiber many hundreds of thou- 
sands of times the length of the cell. A nerve is a bundle of 
nerve fibers. 

The Brain of Man. — In man, as in the frog, the central 
nervous system consists of a rrocop/iu ^— >--^^^^^^^ 
brain and spinal cord inclosed J ^iii^XZ^^^S^-V^C^^^)^'^ 
in a bony case with the nerves f^^}v/r^Th \-\^^^^~^\^ 
leaving it. From the brain, >{~^vJ_^^"V^V^-^^ 
twelve pairs of nerves are u/ ^^^T/^^'^^x^o^'^^y^ 
given off; thirty-one pairs leave f\>0^^^^i>tA.^^ 
the spinal cord. The brain V,^^^^r3_^**'^%sj2:^ 
has three divisions. The cere- Cf^ff^^^^^C"} ^OA/S 
brum (ser'e-brum) makes up ^^v\l/(/Jfim 
the largest part. In this re- ^^^^^O™.-.-™^^^^^ 
spect it differs from the cere- Cf/i^BaiUM mlp^ 
brum of the frog and other ^^ 

vertebrates. It is divided into ^^^ ^^^i^- ^*^ p^^^ separated to show 

7.7 each clearly. 

two lobes, the hemispheres, 

which are connected with each other by a broad band of nerve 
fibers. The outer layer of the cerebrum, which is thrown into 
folds or convolutions, is gray in color, and made up of nerve 
cells and supporting material. The inner part, which is white, 
is composed largely of fibers passing to other parts of the 
brain and down into the spinal cord. Under the cerebrum lies 
the Kttle brain, or cereheVlum. The two sides of the cere- 
bellum are connected by a band of nerve fibers which run 
around into the lower hind-brain or meduVla, This band of 
fibers is called the pons. 



392 NERVOUS SYSTEM AND ORGANS OF SENSE 



Sensory and Motor Nerve Fibers. — Nerves which are con- 
nected with the central nervous system may be made up of 
fibers bearing messages from sense organs in the skin or elsewhere 
to the central nervous system, the sensory fibers, or of other 
fibers which carry impulses from the central nervous system to 
the outside, the motor fibers. Some nerves are made up of both 
kinds of fibers, in which case they are called mixed nerves. 

The Autonomic Nervous System. — The autonomic (or sympathetic) 
nervous system consists of a series of ganglia connected with each other 
and with the central nervous system through some of the spinal and 
cranial nerves, especially the tenth cranial. The autonomic system, both 
in the frog and in man, controls the muscles of the digestive tract and blood 
vessels, the secretions of gland cells, and the heart. 

Functions of the Parts of the Central Nervous System of the Frog. — 
From careful study of Hving frogs, birds, and some mammals we have 
learned much of what we know of the functions of the parts of the central 
nervous system in man. 

It has been found that if the entire brain of a frog is destroyed or 
separated from the spinal cord, " the frog will continue to hve but with a 
very peculiarly modified activity." It does not appear to breathe, nor does 
it swallow. It will not move or croak, but if acid is placed upon the skin 
so as to irritate it, the legs make movements to push away and to clean off 
the irritating substance. The spinal cord is thus shown to be a center for 
defensive movements. If the cerebrum is separated from the rest of the 
nervous system, the frog seems to act a Uttle differently from the normal 
animal. It jumps when touched, and swims when placed in water. It will 

croak when stroked, or swallow if food be placed in 
its mouth. But it manifests neither hunger nor fear, 
and is in every sense a machine which will per- 
form certain actions after certain stimulations. Its 
movements are automatic. If we watch the move- 
ments of a frog which has the brain uninjured in 
any way, we find that the frog acts spontaneously. 
It tries to escape when caught. It feels hungry 
and seeks food. It is capable of voluntary action. 
It acts like a normal individual. 




Regions of the head 



Functions of the Cerebrum. — In gen- 
and action of the different eral, the functions of the different parts of 
parts of the bram. ^j^^ brain in man agree with those we have 

already observed in the frog. The cerebrum has to do with con- 
scious activity. It presides over what we call our thoughts, our 
win, and our sensations. Each part of the area of the outer layer 



REFLEX ACTIONS 



393 




Diagram of the path of a simple nervous reflex action. 



of the cerebrum is given over to some one function, as speech, 
hearing, sight, touch, movements of body parts. The con- 
scious movement of the smallest part of the body has its defi- 
nite locahzed center in the cerebrum. Our knowledge on this 
subject is derived from experiments performed on monkeys, and 
from observations made on persons who had lost the power of 
movement of certain parts .of the body, and were found, 
after death, to have 
had diseases local- 
ized in certain 
parts of the cere- 
brum. 

Reflex Actions; 
their Meaning. — 
If through disease 
or for other reasons 
the cerebrum does 
not function, no 
will power is ex- 
erted, nor are intelligent acts performed. All acts performed 
in such a state are known as reflex actions. An example of a 
reflex may be obtained by crossing the legs and hitting the knee 
a sharp blow. The leg, below the knee, will fly up as a result 
of reflex stimulation. The involuntary brushing of a fly from 
the face and the attempt to move away from the source of an- 
noyance when tickled with a feather, are other examples. In 
a reflex act, a person does not think before acting. The nervous 
impulse comes from the outside to cells that are not in the cere- 
brum. The message is short-circuited back to the surface by 
motor nerves, without ever having reached the thinking centers. 
The nerve cells which take charge of such acts are located in 
the cerebellum or spinal cord. 

Automatic Acts. — Some acts, however, are learned by con- 
scious thought, as writing, walking, running, or swimming. 
Later in life, however, these activities become automatic and 
are controlled by the cerebellum, medulla, and spinal ganglia. 
Thus the thinking portion of the brain is relieved of part of its 
work. 

HUNT. NEW ES. — 26 



394 NERVOUS SYSTEM AND ORGANS OF SENSE 

Habit Formation. — The training of the different areas in the 
cerebrum to do their work efficiently is the object of education. 
When we learned to write, we exerted conscious effort in order to 
make the letters. Now the act of forming the letters is done 
without thought. By training, the act has become automatic. 
In the beginning, a process may take much thought and many 
trials before it is accomplished successfully. After a little prac- 
tice, the same process becomes almost automatic and a habit is 
formed. Habits are really acquired reflex actions. They are the 
result of nature's method of training. The conscious part of 
the brain has trained the cerebellum or spinal cord to do certain 
things that, at first, were taken charge of by the cerebrum. 

Importance of forming Right Habits. — Among the habits 
to be acquired early are the habits of studying properly, of con- 
centrating the mind, of self-control, and above all, of content- 
ment. Get the most out of the world about you. Remember 
that the immediate effect of the study of some subjects in school 
may not be great, but the cultivation of correct methods of 
thinking may be of the greatest importance later in life. 

" The hell to be endured hereafter, of which theology tells, is no worse 
than the hell we make for ourselves in this world by habitually fashioning 
our characters in the wrong way. Could the young but reaUze how soon 
they will become mere walking bundles of habits, they would give more 
heed to their conduct while in the plastic state. We are spinning our own 
fates, good or evil, and never to be undone. Every smallest stroke of 
virtue or of vice leaves its never-so-Uttle scar. The drunken Rip Van Winkle, 
in Jefferson's play, excuses himself for every fresh derehction by saying, 
' I won't count this time! ' Well ! he may not count it, and a kind Heaven 
may not count it; but it is being counted none the less. Down among his 
nerve cells and fibers the molecules are counting it, registering and storing 
it up to be used against him when the next temptation comes. Nothing 
we ever do is, in strict scientific Hteralness, wiped out. Of course this 
has its good side as well as its bad one. As we become permanent drunkards 
by so many separate drinks, so we become saints in the moral, and au- 
thorities in the practical and scientific, spheres by so many separate acts 
and hours of work. Let no youth have any anxiety about the upshot of 
his education, whatever the line of it may be. If he keep faithfully busy 
each hour of the working day, he may safely leave the final result to itself. 
He can with perfect certainty count on waking up some fine morning, 
to find himself one of the competent ones of his generation, in whatever 
pursuit he may have singled out." — James, Psychology. 



TOUCH 



395 



Necessity of Food, Fresh Air, and Rest. — The nerve cells, 
like, all other cells in the body, are continually wasting away and 
being rebuilt. Oxidation of food material is more rapid when 
we do mental work. The cells of the brain, like muscle cells, are 
not only capable of fatigue, but show this in changes of form and 
of contents. Food brought to them in the blood, plenty of fresh 
air, especially when engaged in active brain work, and rest at 
proper times, are essential in keeping the nervous system in 
condition. One of the best methods of resting the brain cells is 
a change of occupation. Tennis, golf, baseball, and other out- 
door sports combine muscular exercise with brain activity of a 
different sort from that of business or school work, thus exer- 
cising other brain cells. 

Necessity of Sleep. — Sleep is an essential factor in the health 
of the brain, especially for growing children. Most brain cells 
attain their growth early in Hfe. Changes occur, however, until 
some time after the school age. Ten hours of sleep should be 
allowed for a child, and at least eight hours for an adult. It 
is during sleep that the brain cells have opportunity to rest and 
store food and energy for their working period. 



The Senses 

Touch. — In animals hav- 
ing a hard outside covering, 
such as certain worms, insects, 
and crustaceans, minute hairs, 
which are sensitive to touch, 
are found growing out from 
the body covering. At the 
base of these hairs are found 
nerve cells which send nerve 
fibers inward to the central 
nervous system. 

Organs of Touch. — In 
man, special nerve endings 
called the tactile corpuscles, which give the sense of touch, are 
located in the skin. The number of tactile corpuscles present 




Nerves in the skin: a, nerve fiber; b, 
tactile papillae, containing a tactile cor- 
puscle; c, papillae containing blood ves- 
sels. (After Benda.) 



396 NERVOUS SYSTEM AND ORGANS OF SENSE 



in a given area of the skin determines the accuracy and ease 
with which objects may be recognized by touch. 

Experiment: Touch. — K you test the different parts of the body, as 
the back of the hand, the neck, the skin of the arm, of the back, or the 
tip of the tongue, with a pair of open dividers, a vast difference in the ac- 
ciu-acy with which the two points may be distinguished is noticed. On the 
tip of the tongue, the two points need be separated by only -^-^ of an inch 
to be distinguished. In the small of the back, a distance of two inches may 
be reached before the dividers feel like two points. 

Temperature, Pressure, Pain. — The sensations of temperature, pressure, 
and pain are determined by different end organs in the skin. Two kinds 
of nerve endings exist in the skin, which give distinct sensations of heat 
and cold. These areas can be located by careful experimentation. There 
are also areas of nerve endings which are sensitive to pressure, and still 
others, most numerous of all, sensitive to pain. 

Taste Organs. — The surface of the tongue is folded into a number of little 
projections known as papillae. In the folds between these papillae on the top 
and back part of the tongue, are located the organs of taste, called taste bvds. 

How we Taste. — Four kinds of substances may be distin- 
guished by the sense of taste. These are sweet, sour, bitter, and 

salt. Certain taste cells located 
near the back of the tongue are 
stimulated only by a bitter taste. 
Sweet substances are perceived by 
cells near the tip of the tongue, 
sour substances along the sides, and 
salt about equally all over the 
surface. A substance must be 
dissolved in order to be tasted. Taste and smell are often 
confused and many things which we believe we taste are in 
reality perceived by the sense of smell. Such 
are spicy sauces and flavors of meats and 
vegetables. That we do not taste certain 
foods is proved easily by holding the nose and 
chewing several different substances, such as 
an apple, an onion, and a raw potato. 

Smell. — The sense of smell is located in 
the membrane lining the upper part of the 
nose. Here are found a large number of rod-shaped cells which 
are connected with the forebrain by means of the olfactory 




Section of circumvallate papilla: 
E, epidermis; T, taste buds; N, 
nerve fibers. 



TASTB CELLS 




SUPP0RTIN9 
CELLS 



Isolated taste bud. 




TASTE, SMELL, HEARING 397 

nerve. In order to perceive odors, it is necessary to have them 
diffused in the air; hence we sniff so as to draw in more air over 
the olfactory cells. 

Outer Ear. — The organ of hearing is the ear. In the fish, 
frog, and reptile, the outer ear, so prominent in man, is entirely 
lacking. The outer ear 

consists of a funnel-like /^,:, Jfe^/br^.^^r^^f"^^^ 

organ composed largely 

of cartilage which is of 

use in collecting sound 

waves' and the auditory l\ '^^ ^^ >a^B^^r^^ g?%-lL^r<?rA^^ 

canal, which is closed at 

the inner end by a tightly %^7 ''^^^^"&^ 

stretched membrane, the f/^^/^cr^ ' ■ m hr ~^^ ' - 

tympan'ic membrane. We >?/7//// 

have seen the tympanic 

membrane of the frog on ^^^^^^^ ""^ ^^"^^^ ^^^• 

the outer surface of the head. The function of the tympanic 

membrane is to receive sound waves, or vibrations in the air, 

which are transmitted, by means of a complicated apparatus 

found in the middle ear, to the inner ear. 

Middle Ear. — The middle ear in man is a cavity inclosed by 
the temporal bone of the skull and separated from the outer 
ear by the tympanic membrane. A little tube called the Eusta- 
chian tube connects the middle ear with the mouth cavity. By 
allowing air to enter from the mouth, the air pressure is equal- 
ized on the tympanic membrane. For this reason, we open the 
mouth at the time of a heavy concussion and thus prevent the 
rupture of the delicate tympanic membrane. Placed directly 
against the tympanic membrane and connecting it with another 
membrane which separates the middle from the inner ear, is a 
chain of three tiny bones, the smallest bones of the body. 
The outermost is called the hammer; the next the incus, or 
anvil; the third the stirrup. All three bones are so called 
from their resemblances in shape to the objects for which they 
are named. These bones are held in place by very small mus- 
cles which are delicately adjusted so as to tighten or relax the 
membranes guarding the middle and inner ear. 



398 NERVOUS SYSTEM AND ORGANS OF SENSE 



The Inner Ear. — The inner ear is one of the most compli- 
cated, as well as one of the most delicate, organs of the body. 
Deep within the temporal l)one there are found two parts, one 
of which is called, collectively, the sctnicircular canals, the other 
the cochlea (kokle-a), or organ of hearing. 

It has been discovered by experimenting with fish, in which 
the semicircular canal region forms the chief part of the ear, 
that this region has to do with the equilibrium or balancing 
of the body. We gain knowledge of our position and our 
movements in space in part by means of the semicircular 
canals. 

That part of the ear which receives sound waves is known as 
the cochlea, or snail shell, because of its shape. This very com- 
plicated organ is lined with sensory cells provided with cilia, 
and its cavity is filled with a fluid. It is believed that some- 
what as a stone thrown into water causes ripples to emanate 
from the spot where it strikes, so sound waves are transmitted 
by means of the fluid filling the cavity to the sensory cells of 
the cochlea and thence to the brain by means of the auditory 
nerve. 

The Eye. — The eye, or organ of vision, is an almost spherical 
body which fits into a socket of bone, the orbit. A stalklike 

structure, the o-ptic nerve, con- 
nects the eye with the brain. 
Free movement is obtained by 
means of six little muscles which 
are attached to the outer coat 
of the eyeball, and to the bony 
socket around the eye. 

The wall of the eyeball is made 
up of three coats. An outer 
tough white coat, of connective 
tissue, is called the sclerot'ic 
coat; this coat is lacking in the 
exposed part of the eyeball, but may be seen by lifting the eye- 
lid. Where the eye bulges out a little in front, the outer coat 
is replaced by a transparent tough layer called the cor'nea. A 
second coat, the choroid (ko'roid), is supplied with blood vessels 




CillaryHusck 



Section of human eye. 



SIGHT 399 

and cells which contain pigments. The i'ris is the part of this 
coat which we see through the cornea as the colored part of the 
eye. In the center of the iris is a small circular hole, called 
the pupil. The iris is under the control of muscles, and may be 
adjusted to varying amounts of light, the hole becoming larger 
in dim light, and smaller in bright light. The inmost layer of 
the eye is called the ret'ina. This is, perhaps, the most delicate 
layer in the entire body. Despite the fact that the retina is 
less than gV of an inch in thickness, there are several layers of 
cells in its composition. The optic nerve enters the eye from 
behind and spreads out over the surface of the ret- 
ina. Its finest fibers are ultimately connected with 
numerous elongated cells which are stimulated by 
light. The retina is dark purple in color, this color 
being due to a layer of cells next to the choroid 
coat and accounts for the black appearance of the 
pupil of the eye, when we look through it into 
the darkened space within the eyeball. The retina 
acts as the sensitized plate in the camera, for on it 
are received the impressions which are transformed Diagram show- 
and sent to the brain and result in sensations of i^s i^ow the lens 

changes its form. 

sight. The eye, like the camera, has a lens. This 
lens is formed of transparent, elastic material. It is directly 
behind the iris, and is attached to the choroid coat by 
means of delicate Hgaments. In front of the lens is a small 
cavity filled with a watery fluid, the a'queous humor, while 
behind it is the main cavity of the eye, filled with a trans- 
parent, ahnost jellylike, vifreous humor. The elasticity of the 
lens permits a change of form and, in consequence, a change of 
focus upon the retina. By means of this change in form, or 
accommodation, we are able to see both near and distant objects 
clearly. 

Defects in the Eye. — In some eyes, the lens is in focus for 
near objects, but is not easily focused upon distant objects; 
such an eye is said to be nearsighted. Other eyes which do not 
focus clearly on objects near at hand are said to be farsighted. 
Still another eye defect is astig'matism, which causes images of 
fines in a certain direction to be indistinct, while images of lines 




400 NERVOUS SYSTEM AND ORGANS OF SENSE 

transverse to the former are distinct. Many nervous troubles, 
especially headaches, may be due to eye strain. 

Experiment ; How we See. — Suppose an object be held in front of the 
eye; rays of light pass from every part of the object and are brought to 
a focus on the retina by means of the transparent lens. You can form an 
image in the same manner by using a reading glass, a box with a hole in 
one end, and a piece of white paper. Notice that the image is inverted. 
The same is true of the image on the retina. When an image is thrown 




Diagram to show how an image is formed in the eye: a, object; b, lens; 

c, image upon retina. 

on the sensory layer, the rods and cones of the retina are stimulated and 
the image is transmitted to the forebrain. We must remember that the 
optic nerve crosses under the brain so that images formed in the right eye 
are received by the left half of the forebrain, and vice versa. 

Care of the Eyes. — Remember that a delicate organ like the 
eye is easily irritated and fatigued. Do not rub the eye, for 
it is easy to introduce germs by means of dirty fingers. If 
any foreign matter like dust gets in the eye, pull the upper lid 
down by means of the eyelashes. If the body is not removed 
by the flow of tears that follows, roll the upper eyelid back over 
a pencil or other small rounded object and remove the foreign 
body with a piece of clean, soft cloth. Boracic acid dissolved 
in warm water makes the best eye wash. 

Fatigue of the eye may be brought about in a number of ways 
in which the tiny muscles of the eye are overtaxed and exhausted. 
Where a bright light falls on white paper and makes a reflection 
the eye becomes tired from trying to shut out some of the light- 



EFFECTS OF ALCOHOL 401 

Too much or too little light is bad, as is reading in a flickering 
light, as on the cars. Especially must we watch a farsighted eye 
for eye strain, as its vision seems perfect but there is a constant 
strain on the part of the muscles of acconmaodation which soon 
results in headache. 

Effects of Alcohol. — We have abeady spoken of alcohol hav- 
ing a paralyzing effect upon the nervous system. This seems 
to be shown in a number of different ways. 

Professor Hodge of Clark University describes many of his own experi- 
ments showing the effect of alcohol on animals. He trained four selected 
puppies to recover a ball thrown across a gymnasium. To two of the dogs 
he gave food mixed with dietetic doses of alcohol, while the others were 
fed normally. The ball was thrown 100 feet as rapidly as recovered. This 
was repeated 100 times each day for fourteen successive days. Out of 
1400 times the dogs to which alcohol had been given brought back the ball 
only 478 times, while the others secured it 922 times. This seems to indi- 
cate that the puppies given alcohol in their diet did not react as quickly 
to the stimulus of the thrown ball as the others did. They were sluggish, 
both mentally and physically. 

Dr. Parkes experimented with two gangs of men, selected to be as 
nearly similar as possible, in mowing. He found that with one gang ab- 
staining from alcohoHc drinks and the other not, the abstaining gang 
could accomphsh more. On transposing the gangs the same results were 
repeatedly obtained. Similar results were obtained by Professor Aschaffen- 
burg of Heidelberg University, who found experimentally that men " were 
able to do 15 per cent less work after taking alcohol." 

The Effect of Alcohol upon Intellectual Ability. — It has been thought 
that alcohol in smaU quantities quickened the mental action, but a long 
series of experiments shows conclusively that this is untrue. KraepeUn 
shows that alcohol lengthens the time taken to perform complex mental work. 

The Drink Habit. — One of the harmful effects of alcohol 
upon those who use it is the formation of the alcohohc 
habit. The first effect of drinking alcoholic Hquors is that 
of exhilaration. After this feeling is gone, for it is a tempo- 
rary state, the subject feels depressed and less able to work 
than before he took the drink. To overcome this feeUng, he 
takes another drink. The result is that before long he finds a 
habit formed from which he cannot escape. With body and 
mind weakened, he attempts to break off the habit. But 
meanwhile his will, too, has suffered from overindulgence. He 
has become a victim of the drink habit! 



402 NERVOUS SYSTEM AND ORGANS OF SENSE 



Self-indulgence, whether in gratification of such a simple de- 
sire as for candy or the more harmful indulgence in tobacco or 
alcoholic beverages, is dangerous — not only in its immediate 
effects on the tissues and organs, but in its more far-reaching 
effects on habit formation. 

The Moral, Social, and Economic Effect of Alcoholic Poison- 
ing. • — In the struggle for existence, it is evident that the man 
whose intellect is the quickest and keenest, whose judgment is 
most sound, is the one who is most likely to succeed. The 

paralyzing effect of alcohol 
upon the nerve centers 
must place the drinker at 
a disadvantage. In a hun- 
dred ways, the drinker 
sooner or later feels the 
handicap that the habit of 
drink has imposed upon 
him. Who knows the num- 
ber of railway accidents 
that have been due to the 
uncertain eye of some en- 
gineer who mistook his 
signal? 

In business and in the 
professions, the story is the 
same. The abstainer wins 
over the drinking man. 

Not alone in activities o) 
life, hut in the length of life, 
has the abstainer the ad- 
vantage. Figures presented by life insurance companies show 
that the nondrinkers have a considerably greater chance of long 
life than do drinking men. So decided are the results shown by 
those figures that several companies have lower premiums for 
nondrinkers than for the drinkers who insure with them. 

It is the economic argument that largely won the fight for 
prohibition that resulted in the Eighteenth Amendment. Think- 
ing people all over the United States began to realize the 




Proportion of crime due to alcohol in various 
countries. 



ALCOHOLIC POISONING 403 

harm that the abuse of Hquor wrought on the nation. Follow- 
ing the enforcement of the prohibition law, we find example 
after example of better economic conditions. Money which 
formerly went for drink is now used for better food and niore 
of it, for useful and helpful articles in the home, for the purchase 
of homes and for investment and saving. 

Summary. — It would be impossible to sum up in a few 
words the contents of this chapter. We have seen that the 
nervous system through its sense organs (as the eye, ear, and 
organs of pressure, touch, heat, cold, and taste) informs us con- 
cerning our environment. The central nervous system directs 
and coordinates action through the sensory and motor nerves 
and the brain. There is also an autonomic system which takes 
care of the body functions not under our control. 

Problem Questions. — 1. What is the work of the central 
nervous system? of the autonomic nervous system? How 
have these facts been proved? 

2. What are the functions of the cerebrum? the cerebellum? 
the spinal cord? 

3. What is a neuron? 

4. What is a reflex? Explain fully. 

5. How are habits formed? 

6. What are sensations? What are sense organs? 

7. How do we taste? hear? see? 

8. What are some eye defects and how may they be cor- 
rected? 

9. What are the chief reasons against the use of alcohol from 
the standpoint of the nervous system? 

Peoblem and Project References 

Davison, The Human Body and Health. American Book Company'. 

Gulick, Control of Body and Mind. Ginn and Company. 

Hough and Sedgwick, The Human Mechanism. Ginn and Company. 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Martin, The Human Body. Henry Holt and Company. 

Ritchie, Human Physiology. World Book Company. 

Sharpe, A Laboratory Manual. American Book Company. 

Starling, Human Physiology. Lea and Febiger. 



XXIX. GOOD HEALTH AND HOW TO. KEEP IT 

Problem. A study of personal hygierie. (Laboratory Manual, 
Proh. LVI; Laboratory Problems, Probs. 234 to ^49.) 

Health and Disease. — In previous chapters we have con- 
sidered the body as a machine more deHcate in its organiza- 
tion than the best-built mechanism made by man. In a state 
of health this human machine is in good condition; disease 
is a condition in which some part of the body is out of order, 
thus interfering with the smooth running of the mechanism. 

Personal Hygiene. — It is the purpose of the study of hygiene 
to show us how to live so as to keep the body in a healthy 
state. Hygiene not only prescribes certain laws for the care of the 
various parts of the body, — the skin, the teeth, the food tube 
and the sense organs, — but it also shows us how to avoid dis- 
ease. The foundation of health later in life is laid down at 
the time we are in school; for that reason, if for no other, a 
knowledge of the laws of hygienic living is necessary for all 
school children. Unlike some of the lower animals, we can 
change or modify our immediate surroundings so as to make 
them better and more hygienic places to live in. Hygienic 
conditions in homes and around them should be improved as we 
learn more about the value of a sanitary environment. It is the 
purpose of this chapter to show how we may do our share to 
cooperate with those in charge of the public health in our towns 
and cities. 

Some Methods of Prevention of Disease. — The proverb, 
" An ounce of prevention is worth a pound of cure," has much 
truth in it. Disease is largely preventable. Fresh air, the 
needed amount of sleep, moderate exercise, and pure food 
and water are essentials in hygienic living and in escape from 
disease. 

Pure Air Needed. — What do we mean by fresh air, and why 
do we need it? We have already seen that oxidation takes 

404 



PURE AIR 



405 



place within the body, and that air receives the carbon dioxide 
which is given off as a product of respiration. In addition to 
the carbon dioxide, water vapor and heat are given off as well as a 
very small amount of organic material of a poisonous nature. 
It is the presence of this material that gives rise to the odor 
noticeable in a close room. But other organic material is 
found in air. Dust from the street contains bacteria of many 
kinds, some of which may be disease-producing. Thus may be 
spread bacteria from the respiratory tracts of people who have 









■j 








1 






E^^^"^ 


M 








^1 








^m 


^^^^^ 






m| 


^m^^^^g^ 




^^^liS 


In 


j|||||iB^^^ ^ 




^ 


1 


■HhHII^^.-.. 


. ^ 


„ 


^m 




A. B. 

Two cultures. A was exposed to the air of a dirty street in the crowded part of 
Manhattan. B was exposed to the air of a well-cleaned and watered street in 
the uptown residence portion. Which culture has the more colonies of bacteria? 
How do you account for this? 

colds, pneumonia, diphtheria, or tuberculosis. Much of the dust 
is dried excreta of animals. Soft-coal smoke does its share to 
add to the impurities of the air, while sewer gas and illuminat- 
ing gas are frequently found in sufficient quantities to poison 
people. Pure air is, as can be seen, almost an impossibility in 
a great city. 

How to get Fresh Air. — As we know, green plants give off 
in the sunlight considerably more oxygen than they use, and 
they take in carbon dioxide. The air in the country is naturally 
purer than in the city, as smoke and bacteria are not so preva- 
lent there, and the numerous plants give off oxygen. In the 
city the night air is purer than day air, because the fac- 
tories have stopped work, the dust has settled, and fewer 



406 GOOD HEALTH AND HOW TO KEEP IT 



people are on the streets. The old myth that " night air " is 
injurious has long since been given up, and thousands of people 
of delicate health, especially those who have weak throats or 
lungs, are regaining health by sleeping out of doors or with the 
windows wide open. It is essential in sleeping out of doors 
or in a room with a low temperature that the body be kept 
warm and the head be protected from strong drafts by a night- 
cap or hood. Proper ventilation at all times is one of the 
greatest factors in good health. 

Change of Air. — Persons in poor health, especially those hav- 
ing tuberculosis, are often cured by a change of air. This is 
not always due so much to the composition of the air as to 
change of occupation, rest, and good food. Mountain air is 
dry, and relatively free from dust and bacteria, and often helps 
a person having tuberculosis. Air at the seaside is beneficial 
for some forms of disease, especially hay fever and bone tuber- 
culosis. Many sanitariums 
have been established for 
this latter disease near the 
ocean, and thousands of lives 
are being saved in this way. 
The Relation of Pure 
Food and Pure Water to 
Health. — Thanks to the 
care of state and city govern- 
ments there is little need 
nowadays for the health of 
any individual to suffer from 
impure food or water. But 
that people do become sick 
and die from such causes 
every day is well known, as 
is shown by the many cases of typhoid fever, summer com- 
plaint, and ptomaine poisoning of various sorts. Our milk may 
have been watered or sent in cans washed with water containing 
typhoid germs, we may eat oysters bred in contaminated lo- 
calities, we may. have received and eaten fruits or vegetables 
sprinkled with water containing the germs. Our laws, however 




Tracks of germs left by a fly crawling on 
* sterilized media in a dish. * 



EXERCISE AND SLEEP 407 

good, cannot cope with human carelessness. Not only should 
we as individuals demand from the source of supply pure 
food and water, but we should do our share at home to keep 
them pure. Flies and other insects shpuld be prevented from 
reaching food. Vegetables and fruits must not be eaten in 
an unripe or half-rotten condition, nor should the latter be 
canned or preserved. All raw fruits and vegetables should 
be either peeled or washed before eating. In general, foods 
may be made safe to eat by cooking long enough to kill the 
germs. Milk to be rendered absolutely safe should be pas- 
teurized (so called after Louis Pasteur, the originator of the 
process), that is, heated to 160° Fahrenheit for 20 minutes. 
Ptomaine poisoning is often caused by bacteria in canned 
material which were not killed in the cooking and which act upon 
the proteins causing them to form poisons or ptomaines. Such 
foods are dangerous, for cooking does not destroy the poison. 
Meats which have been hung so long as to have an odor, 
and cold storage meats that appear to be decayed, should be 
avoided. 

Relation of Proper Exercise and Sufficient Sleep to Health. — 
We are all aware that exercise in moderation has a beneficial 
effect upon the human organism. The pale face, drooping 
shoulders, and narrow chest of the boy or girl who takes no 
regular exercise are too well known. Exercise, besides giving 
work to the muscles, increases the activity of the heart and lungs, 
causing deeper breathing; it liberates heat and carbon dioxide 
from the tissues where the work is taking place, thus increasing 
the respiration of the tissues themselves, and aids mechanically 
in the removal of wastes from tissues. It is well known that 
exercise, when taken some little time after eating, has a very 
beneficial effect upon digestion. Exercise and games, especially 
if a change of occupation, are of immense importance to the 
nervous system as a means of rest. The increasing number of 
playgrounds in this country is due to this acknowledged need 
of exercise for growing children. 

Proper exercise should be moderate and varied. Walking in 
itself is a valuable means of exercising certain muscles, and so is 
bicycling, but neither is ideal as the only form to be used. Vary 



408 GOOD HEALTH AND HOW TO KEEP IT 

your exercise so as to bring different muscles into play, take 
exercise that will allow free breathing out of doors if possible, 
and the natural fatigue which follows will lead to the rest and 
sleep that every normal body requires. 

Sleep is one way in which all cells in the body and particularly 
those of the nervous system get their rest. The nervous system, 
by far the most delicate and hardest worked set of tissues in the 
body, needs rest more than do other tissues, for its work direct- 
ing the body ends only with sleep or unconsciousness. The 
afternoon nap, snatched by the brain worker, gives him re- 
newed energy for his evening's work. It is not hard applica- 
tion to a task that wearies the brain; it is continuous work 
without rest. 

Effect of Alcohol on the Ability to Resist Disease. — Among 
certain classes of people the behef exists that alcohol in the 
form of wine, beer, brandy, or some other drink, or in patent 
medicines, rhalt tonics, and the like, is of great importance in 
building up the body so as to resist disease or in curing it after 
disease has attacked it. Nothing is farther from the truth. 
In experiments on over three hundred animals, including dogs, 
rabbits, guinea pigs, fowls, and pigeons, Laitenen of the Uni- 
versity of Helsingfors and Professor Frankel of Halle found 
that alcohol without exception made these animals more sus- 
ceptible to disease than were the controls. 

Use of Alcohol in the Treatment of Disease. — In the Lon- 
don Temperance Hospital alcohol was prescribed seventy-five 
times in thirty-three years. The death rate in this hospital 
has been lower than that of most general hospitals. One of the 
most serious misconceptions is that alcohol helps people who 
have tuberculosis to fight that disease successfully. Nothing 
is farther from the truth. 

In a paper read at the International Congress of Tubercu- 
losis, in New York, 1906, Dr. Crothers reported that alcohol 
as a remedy or a preventive medicine in the treatment of 
tuberculosis is a most dangerous drug, and that all prepara- 
tions of sirups containing spirits increase, rather than diminish, 
the disease. 

Professor Guttstadt of Berlin publishes statistics showing; 



EFFECTS OF ALCOHOL 



409 



that in Prussia of every 1000 deaths of men over twenty-five 
years, 161 are from tuberculosis. Of every 1000 deaths among 
bartenders, 556 are from tuberculosis; among brewery em- 
ployees, 345; school-teachers, 143; physicians, 113; clergy, 76. 
The fifty-fifth annual report of the British Registrar General 
gives the average death rate of England as 13 per thousand, but 
among brewers it is 41 per thousand, only four occupations 
showing a higher rate. 

Experience of Insurance Companies. — The United Kingdom 
Temperance and General Provident Institution of London in- 
sures in two departments, a general section and one for total ab- 
stainers- During the 60 years from 1841 to 1901 there were 
31,776 whole-life policies in the general or nonabstaining sec- 
tion. These passed through 446,943 years of Hfe, and there were 
8947 deaths. In the abstaining section there were 29,094 whole- 
life policies, passing through 398,010 years of life, with 5124 
deaths. If the death rate in the abstaining section had equaled 
that in the general section, there would have been 6959 deaths 
instead of 5124. In other words, the mortality averaged 36 
per cent higher in the nonabstaining section than in the 
abstaining section. 



JL 



2P 



JL 



,^ 53,044 
liveto/OYrs. 



Of 100,000 
Non drinkers 

aged20yrs, 

OfmOOO I 42,/09 



40 



JSL. 



60 



7.0 



SO 



90 



46.956 
die earlier 



57,981 
die earlier 



10 20 30 40 SO 60 TO 

Effect of drinking upon probability of long life. 



80 



90 



100 



100 



In an article published in a book by Horsley and Sturge, 
Dr. Arthur Newsholme shows that of 100,000 total abstainers 
starting at the age of 20 years, 53,044 reach 70 years, while 
46,956 die before 70 years; but of 100,000 moderate drinkers 
starting at 20, 42,109 reach 70 years, while 57,891 die before 
70 years. 

In the Scottish Temperance Life Assurance Society, in the 



HUNT. NEW E8. — 97 



410 GOOD HEALTH AND HOW TO KEEP IT 

twenty years ending 1897, the deaths amounted to 69 per cent 
of the expected mortaHty in the general section, while in the 
total abstainers' section they amounted to only 47 per cent of 
the expected number. The number of deaths in the general 
section of the Sceptre of Life Association, England, was 80.34 
per cent of the expectation in the fifteen years ending 1898, 
but in the total abstainers' section it was only 56.37 per cent 
of the expected mortaUty. 

In considering the statistics of the insurance companies, it is 
well to remember that those insured in the general sections were 
picked men as well as those in the total abstainers' sections. 

In discussing the experience of fraternal societies, Dr. News- 
holme gives the following statistics from the report of the Pub- 
lic Actuary of South AustraHa: — 

Average Mor- Average 

TAiiiTY Per Sickness in 

Cent Weeks 

Abstainers' Societies 0.689 1.248 

Nonabstainers' Societies 1.381 2.317 

Mortality Per Average Weeks op 

Cent op Sick Sickness per Each 

Members Member Sick 

Abstainers' Societies 3.557 6.45 

Nonabstainers' Societies 6.532 10.91 

Attention should be called to the fact that the nonabstain- 
ers' societies have many members who are total abstainers, 
but, unlike the abstainers' societies, they do not refuse to ad- 
mit nonabstainers. The number of weeks of sickness in the 
table refers to the average number of weeks for which the 
members call upon the sick fund of the society. All of these 
facts quoted prove that from the standpoint of health as well 
as economically alcohol is a menace. 

Rules of Hygiene. — The following are rules of individual 
hygiene as summarized by Professor Irving Fisher, of Yale. 

Air 

Keep out of doors as much as possible. 

Breathe through the nose, not through the mouth. 

When indoors, have the air as fresh as possible — 

(a) By having aired the room before occupancy. 

(6) By having it continuously ventilated while occupied. 



RULES OF HYGIENE 411 

Not only purity, but coolness, dryness, and motion of the air, if not very 
extreme, are advantageous. Air in heated houses in winter is usually too 
dry, and may be humidified with advantage. 

Clothing should be sufficient to keep one warm. The minimum that will 
secure this result is the best. The more porous your clothes, the more 
the skin is educated to perform its functions with increasingly less need 
for protection. Take an air bath as often and as long as possible. 

Water 

Take a daily water bath, not only for cleanliness, but for skin gym- 
nastics. A cold bath is better for this purpose than a hot bath. A short 
hot followed by a short cold bath is still better. In fatigue, a very hot 
bath lasting only half a minute is good. 

A neutral bath, beginning at 97° or 98°, dropping not more than 5°, 
and continued 15 minutes or more, is an excellent means of resting the 
nerves. 

Be sure that the water you drink is free from dangerous germs and 
impurities. ' " Soft " water is better than " hard " water. Ice water 
should be avoided unless sipped and warmed in the mouth. Ice may 
contain spores of germs even when germs themselves are killed by cold. 

Cool water drinking, including especially a glass half an hour before 
breakfast and on retiring, is a remedy for constipation. 

Food 

Teeth should be brushed thoroughly several times a day, and floss silk 
used between the teeth. Persistence in keeping the mouth clean is good 
not only for the teeth, but for the stomach. 

Masticate all food up to the point of involuntary swallowing, with the 
attention on the taste, not on the mastication. Food should simply be 
chewed and relished, with no thought of swallowing. There should be 
no more effort to prevent than to force swallowing. It will be found that 
if you attend only to the a^eeable task of extracting the flavors of your 
food, nature will take care of the swallowing, and this will become, Hke 
breathing, involuntary. The more you rely on instinct, the more normal, 
stronger, and surer the instinct becomes. The instinct by which most 
people eat is perverted through the " hurry habit " and the use of abnor- 
mal foods. Thorough mastication takes time, and therefore one must 
not feel hurried at meals if the best results are to be secured. 

Sip Uquids, except water, and mix with sahva as though they were 
soUds. 

The stopping point for eating should be at the earliest moment when 
one is really satisfied. 

The frequency of meals and time to take them should be so adjusted 
that no meal is taken before a previous meal is weU out of the way, in 



412 GOOD HEALTH AND HOW TO KEEP IT 

order that the stomach may have had time to rest and prepare new juices. 
Normal appetite is a good guide in this respect. One's best sleep is on an 
empty stomach. Food puts one to sleep by diverting blood from the head, 
but disturbs sleep later. Water, however, or even fruit may be taken 
before retiring without injury. 

An exclusive diet is usually unsafe. Even foods which are not ideally 
the best are probably needed when no better are available, or when the 
appetite especially calls for them. 

The following is a very tentative list of foods in the order of excellence 
for general purposes, subject, of course, to their palatability at the time 
eaten: fruits, nuts, grains (including bread), butter, buttermilk, salt in 
small quantities, cream, milk, potatoes, and other vegetables (if fiber is 
rejected), eggs, custards, digested cheeses (such as cottage cheese, cream 
cheese, pineapple cheese, Swiss cheese, Cheddar cheese, etc.), curds, whey, 
vegetables (if fiber is swallowed), sugar, chocolate, and cocoa, putrefactive 
cheeses (such as Limberger, Rochefort, etc.), fish, shellfish, game, poultry, 
meats, liver, sweetbreads, meat soups, beef tea, bouillon, meat extracts, 
tea and coffee, condiments (other than salt), and alcohol. None of these 
should be absolutely excluded, unless it be the last half dozen, which, with 
tobacco, are best dispensed with for reasons of health. Instead of exclud- 
ing specific food, it is safer to follow appetite, merely giving the benefit of 
the doubt between two foods, equally palatable, to the one higher in the 
list. In general, hard and dry foods are preferable to soft and wet foods. 
Use some raw foods — nuts, fruits, salads, milk, or other — daily. 

The amount of protein required is much less than ordinarily consumed. 
Through thorough mastication the amount of protein is automatically re- 
duced to its proper level. 

The sudden or artificial reduction in protein to the ideal standard is 
apt to produce temporarily a " sour stomach," unless fats be used abun- 
dantly. 

To balance each meal is of the utmost importance. When one can trust 
the appetite, it is an almost infallible method of balancing, but some 
knowledge of foods will help. The aim, however, should always be — 
and this cannot be too often repeated — to educate the appetite to the 
point of deciding all these questions automatically. • 

Exercise and Rest 

The hygienic life should have a proper balance between rest and exer- 
cise of various kinds, physical and mental. Generally every muscle in the 
body should be exercised daily. 

Muscular exercise should hold the attention, and call into play will 
power. Exercise should be enjoyed as play, not endured as work. 

The most beneficial exercises are those which stimulate the action of 
the heart and lungs, such as rapid walking, running, hill climbing, and 
swimming. 



RULES OF HYGIENE 413 

The exercise of the abdominal muscles is the most important in order to 
give tone to those miLscles and thus aid tlie portal circulation. For the 
same reason erect posture, not only in standing, but in sitting, is im- 
portant. Support the hollow of the back by a cushion or otherwise. 

Exercise should always be hmited by fatigue, which brings with it 
fatigue poisons. This is nature's signal when to rest. If one's use of diet 
and air is proper, the fatigue point will be much farther off than other- 
wise. 

One should learn to relax when not in activity. The habit produces 
rest, even between exertions very close together, and enables one to con- 
tinue to repeat those exertions for a much longer time than otherwise. 
The habit of lying down when tired is a good one. 

The same principles apply to mental rest. Avoid worry, anger, fear, 
excitement, hate, jealousy, grief, and all depressing or abnormal mental 
states. This is to be done not so much by repressing these feelings as by 
dropping or ignoring them — that is, by diverting and controlling the atten- 
tion. The secret of mental hygiene Hes in the direction of attention. 
One's mental attitude, from a hygienic standpoint, ought to be optimistic 
and serene, and this attitude should be striven for not only in order to pro- 
duce health, but as an end in itself, for which, in fact, even health is prop- 
erly sought. In addition, the individual should, of course, avoid infection, 
poisons, and other dangers. 

Occasional physical examination by a competent medical examiner is ad- 
visable. In case of illness, competent medical treatment should be sought. 

Finally, the duty of the individual does not end with personal hygiene. 
He should take part in the movements to secure better pubHc hygiene 
in city, state, and nation. He has a selfish as well as an altruistic motive 
for doing this. His air, water, and food depend on health legislation and 
administration. 

All the foregoing rules are important. The results which 
may be obtained by following them depend largely on the 
thoroughness with which they are followed. This is true es- 
pecially of fresh air and mastication. If all the rules are 
followed and followed thoroughly, including the one most com- 
monly neglected, — namely, keeping within the fatigue limit, 
— the average man may reasonably expect to add greatly to his 
length of life, his activity per day, his satisfactions, and his 
usefulness. The laws of " humaniculture " can be depended 
upon as much as those of agriculture, horticulture, or stock 
raising. 

Summary. — The human machine, In order to do its most 
efficient work, must be properly cared for. This chapter has 



414 GOOD HEALTH AND HOW TO KEEP IT 

given us some suggestions. Pure air and plenty of it, sun- 
light, pure food and water, a dietary selected from the best of 
foods given on page 412, rest and recreation as well as work 
and a careful following out of Dr. Fisher's laws of health will go 
far toward making each one of us healthy and happy. 

Problem Questions. — 1. What has fresh air to do with 
health? 

2. How can we get fresh air best in large cities? 

3. What is pure water? How can we be sure it is pure? 

4. What is pure milk and how can it be obtained? 

5. What is the relation of exercise to health? 

6. What is the relation of alcohol to health as proved by 
statistics? 

7. Make up a balanced diet for yourself for one week. Why 
choose the foods you have taken? 

8. What is fatigue? How does it cause trouble to a young 
person ? 

Problem and Project References 

Bergey, Principles of Hygiene. W. B. Saunders Company. 

Broadhurst, Home and Community Hygiene. J. B. Lippincott Company. 

Chapin, Health First. The Century Company. 

Fisher and Fisk, How to Live. Funk and Wagnalls Company. 

Hazen, Clean Water and How to Get It. Wiley. 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Hunter and Whitman, Civic Science. American Book Company. 

Lee, Health and Disease. Little, Brown and Company. 

Pyle, Personal Hygiene. W. B. Saunders Company. 

Sherman, Chemistry of Food and Nutrition. The Macmillan Company, 

Sharpe, A Laboratory Manual. American Book Company. 



XXX. HEALTH AND DISEASE. A CHAPTER ON 

CIVIC BIOLOGY 

Problem. How the civic authorities protect us from disease. 

Public Sanitation and Hygiene. — To-day, as never before, 
people are beginning to realize their part in the campaign against 
disease. Not only is the teaching of hygiene required in our 
schools but much practical health work is being done by the 
boys and girls in the schools. High school boys and girls have 
organized anti-fly and anti-mosquito campaigns which have 
resulted in the stamping out of diseases carried by flies and of 
malaria in some communities. High school boys and girls have 
organized sanitary and service squads which have resulted in 
better sanitary conditions in schools and school grounds. High 
school boys and girls have taken the inspiration for healthy 
living from their biology laboratories to their homes and have 
planted in them the seeds of practical hygiene and sanitation. 
This chapter may help other boys and girls to do their part in 
making conditions better in their communities. 

The Work of the Department of Street Cleaning. — In any 
city one menace to the health of its citizens exists in the refuse 
and garbage. The city streets, when dirty, contain countless 
millions of germs which have come from decaying material, or 
from people ill with contagious diseases. In large cities a depart- 
ment of street cleaning not only cares for the removal of dust 
from the streets, but also has the removal of garbage, ashes, and 
other waste as a part of its work. The practice of putting 
open cans containing ashes and garbage into the street for 
removal is an indirect means of spreading disease, for flies breed 
and germs thrive in them. The street-cleaning department 
should be aided by every citizen; rules for the separation of 
garbage, papers, and ashes should be kept. Garbage and ash 
cans should be covered. The practice of upsetting ash or garbage 

415 



116 



HEALTH AND DISEASE 



cans is one which no young citizen should allow in his neigh- 
borhood, for sanitary reasons. The best results in street-clean- 
ing in summer are obtained by washing or flushing the streets, 
for thus the dirt containing germs is prevented from getting 
into the air. The garbage is removed in carts, and part of it 
is burned in huge furnaces. The animal and plant refuse is 
cooked in great tanks; from this material the fats are ex- 




A style of truck for collecting rubbish (on top) and garbage or ashes (below). 

tracted, and the solid matter is sold for fertilizer. Ashes are 
used for filhng marsh land. Thus the removal of waste matter 
may pay for itself in a large city. 

The Necessity of a Pure Milk and Water Supply. — The city 
of New York has spent hundreds of milHons of dollars to 
bring a supply of pure water to her citizens. Other cities are 
doing the same. The world has awakened to the necessity of a 
pure water supply, largely because of the number of epidemics 
of typhoid which have been caused by contaminated water. 
Typhoid fever germs live in the food tube, hence the excreta of 
a typlioid patient contain large numbers of germs wliich often 
pass from the sewers into the drinking water. Many cities take 



MILK AND WATER SUPPLY 



417 



their water supply directly 
from rivers, sometimes not 
far below another large 
town. Such cities are in 
danger of having their wa- 
ter supply polluted. Some 
cities on very large lakes 
take their supply of water 
from the lakes into which 
their sewage flows. In cities 
which drain their sewage 
into rivers and lakes, the 
question of maintaining 
sanitary conditions is a 
large one, and many cities 
now have means of dispos- 
ing of their sewage so that 
it is harmless to their 
neighbors. Filtering pol- 
luted water by passing it 
through settling basins and 
sand filters removes about 
98 per cent of the germs. 
The results of drinking un- 
filtered and filtered water 
in certain large cities are 
shown graphically in the 
diagram. In addition to 
filtering, some cities add 
chlorine to their water in 
very minute quantities but 
enough to kill all harmful 
germs. Thus water from 
impure sources is made fit 
to drink. 

In the country typhoid 
may be spread by the germs 
getting into a well or spring 




Growth of bacteria in a drop of im- 
pure water allowed to run down a steril 
ized culture in a dish. 




Cases of typhoid per 100,000 inhabitants 
before filtering water supply (solid) and after 
(shaded) in A, Watertowii, N. Y.; B, Albany, 
N. Y.; C, Lawrence, Mass.; D, Cincinnati, O. 
What is the effect of filtering the water supply? 



418 



HEALTH AND DISEASE 



from which the supply of water comes. This may be avoided 
by having privies and cesspools some distance from the well or 
spring and so placed that they drain away from it. Wells should 
have a cemented cap around the top so as to keep out surface 
water. The deeper water is less dangerous, as germs rarely Hve 
long more than five feet below ground. 

Serious outbreaks of typhoid have been traced to contam- 
inated milk supplies. A case of typhoid exists on a farm; the 
sewage gets into the well from which water is used for the 
washing of milk cans. Typhoid germs thrive in the milk. Thus 



^?AJ9M A 



\ 



• 

•••• •••• 




•• •••• 




• 




•• • ••• 




► - 




















* 






• •••••• 

• • •• • 




•• •••• 

• 

• ••••• 




••• 

• 

••• 


• ••• 

• • 




• 
• 

• 

• •••• • 



■ •• •••••• 



A L^J I 1 




♦—*• 



J^AftM B 



• • • •• • • 



How typhoid may spread. Each square represents a city block, 
and each black dot represents a case of typhoid in houses sup- 
plied with milk from Farms A and B. There is a case of typhoid 
at Farm A. The cans from B are washed at A and returned to B. 



the milkman spreads disease. The diagram on this page illus- 
trates a recent epidemic, which was traced to a farm on which 
was a person having typhoid. 

Railroads are often responsible for spreading typhoid. It is 
said that an outbreak of typhoid in Scranton, Pa., was due to 
the fact that the excreta from a typhoid patient traveling in a 
sleeping car were washed by rain into a reservoir near which 
the train was passing. Railroads are thus seen to be great open 
sewers. A sanitary car toilet should be provided so that filth 
and disease will not be scattered over the country. 



BOARDS OF HEALTH 419 

Work of a Board of Health. — Although it is absolutely 
necessary for each individual to obey the laws of health if he 
or she wishes to keep from disease, it has also become neces- 
sary, especially in large cities, to have general supervision over 
the health of people Hving in a community. This is done by 
means of a department or board of health which cares for pub- 
He health. A Hst of regulations and laws known as the Sani- 
tary Code is given out to the citizens. These regulations concern 
the care of buildings and plumbing, the cleanliness of street cars 
and other public vehicles, the protection and supervision of foods 
sold, the inspection of our suppHes of milk and water, and, par- 
ticularly, the control of contagious diseases. 

How the Board of Health fights Typhoid and Other Dis- 
eases. — Pure water is the first essential in preventing epi- 
demics of typhoid. Health board ofl&cials are constantly test- 
ing the water supply, and if any harmful bacteria appear 
the water is chlorinated and a warning is sent out to boil the 
water. Boiling water for 10 minutes kills harmful germs. 

The milk supply is also subject to rigid inspection. Milk 
brought into a city is tested, not only for the amount of cream 
present to prevent dilution with water, but also for the pres- 
ence of germs. The cleanliness of the cans, wagons, etc., is 
also watched. The cows are also tested to see if they have 
tuberculosis, for infected cows might spread the disease to 
human beings. 

During the summer months many babies die from diarrhoea. 
This disease is spread almost entirely through impure milk, 
which often becomes infected by flies carrying the germs to it. 
Spread of diseases through milk can be prevented by careful 
pasteurization (heating to 160° F. for 20 minutes). In many 
large cities pasteurized milk is sold at a reasonable price to 
poor people, and thus much disease is prevented. 

How the Board of Health fights Tuberculosis. — Tubercu- 
losis, which a few years ago killed fully one seventh of the 
people who died from disease in this country, now kills less 
than one tenth. This decrease has been largely brought about 
because of the treatment of the disease. Since it has been 
proved that tuberculosis if treated early enough is curable, by 



420 



HEALTH AXD DISEASE 



quiet Kving, good food, and 29?€7?/?/ of fresh air and light, we 
find that numerous sanatoria have come into existence which 
are supported by private or pubhc means. At these sanatoria 
the patients live out of doors, and sleep in the open ah^, while 
they have plenty of nourishing food and httle exercise. By 
tenement-house laws which require proper air shafts and win- 
dow ventilation in dweUings, by laws against spitting in pub- 
He places, and in many other ways, the boards of health 
in our towns and cities are waging war on tuberculosis. 




Tuberculosis Camp, Raybrook Sanatorium, New York. Patients live in the open 
air the year round, with open tents for shelter. 

Diseases Carried by Food. — Disease germs of various sorts, 
typhoid, tuberculosis, scarlet fever, diphtheria, and many others 
ma}' be transferred through the agency of food. Fruits and 
vegetables maj^ be carriers of disease, especially if they are sold 
from exposed stalls or carts and handled b}' the passers-b3^ All 
vegetables, fruits, or raw foods should be carefully washed 
before using. Spoiled or overripe fruit, as well as meat which 
is decayed, is swarming with bacteria and should not be used. 
The board of health has super\'ision over the sale of fruit; 



BOARDS OF HEALTH 421 

meats, fish, etc., and frequently in large cities food unfit for 
sale is condemned and destroyed. 

Infectious Diseases; Quarantine and Disinfection. — One 

of the important means for preventing the spread of diseases 
caused by bacteria or protozoa is by quarantine, or isolation of 
the person who has the disease. No one save the doctor and 
nurse should enter the room of the person quarantined. After 
the disease has run its course, the clothing, bedding, etc., in the 
sickroom should be disinfected by boiling in soapy water. The 
patient should be washed carefully, including the mouth, face 
and hair, and should be dressed in sterile clothes before being 
allowed to see people again. The room should be thoroughly 
cleaned and the woodwork washed with hot soapy water. In this 
way disease germs are destroyed and the danger of contagion is 
prevented. 

Immunity. — To prevent germ diseases we must kill many of the 
germs by attacking them directly with poisons (the poisons thus 
used are called germicides or disinfectants), and we must keep 
in such condition that we do not take disease when we come in 
contact with the germs that cause it. This insusceptibility or 
immunity may be either natural or acquired. Natural immunity 
seems to be in the constitution of a person, and may be inherited. 
It is racial, some races being more and others less susceptible 
to certain diseases. Natural immunity may be reduced by ex- 
posure to unfavorable conditions of temperature, by lack of proper 
food, by unsanitary living or working conditions and, in particu- 
lar, by fatigue. This shows the importance of careful living on 
the part of each one of us. Immunity for some diseases may be 
acquired by means of antitoxin, as in diphtheria. This treatment, 
as the name denotes, is a method of neutralizing the poison 
(toxin) caused by the bacteria in the system. It was discovered 
by a German, Von Behring, that the serum of the blood of an 
animal immune to diphtheria is capable of neutrahzing the poison 
produced by the diphtheria-causing bacteria in people. Horses 
develop large quantities of antitoxin when given the diphtheria 
toxin or poison. The serum (or liquid part) of the blood of these 
horses is then used to inoculate the patient suffering from or 
exposed to diphtheria, and thus the disease is checked or prevented 



422 



HEALTH AND DISEASE 



IJUrriber qf Deathspw- loo 
cases o''jDij*ttK.eria, -wKeru 
flntito%ii\ 14 used, oiv Sj^Crf^t-* 

•^Lstloy No DecftKs 




Antitoxin must be 
used in the early stages 
of diphtheria to be of 
value. 



altogether. This is known as artificial immunity. By the toxin- 
antitoxin treatment, immunity to diphtheria can be given to those 

who have not been exposed to the disease. 
The Schick test determines at any time 
whether a child is already immune : a very 
small amount of diphtheria toxin is placed 
under the skin of the arm, and the spot will 
turn red if the child is not immune. 

Vaccination. — Smallpox was once the 
most feared disease in this country ; 95 per 
cent of the people suffered from it. As late 
as 1898, over 50,000 persons a year in Russia 
lost their lives from this disease. It is a 
contagious disease, probably not caused by bacteria, but by an 
animal germ. Smallpox has been brought under absolute con- 
trol by vaccination with the substance (called virus) which causes 
cowpox in a cow. Cowpox is like a mild form of smallpox, and 
the introduction of this virus gives a person complete immunity 
to smallpox for several years after vaccination. This immunity 
is caused by the formation of a germicidal substance in the blood, 
due to the introduction of the vaccine containing the weakened 
virus. Vaccination was first tried by the English physician 
Jenner, who noted that dairymaids who had had cowpox did not 
take smallpox. 

Vaccination for typhoid and paratyphoid is now practiced 
almost universally. Since the World War it has 
been proved that man can be kept free from 
these diseases, which in our Spanish-American 
War killed many times more soldiers than did 
Spanish bullets. This type of vaccination con- 
sists in introducing into the body the dead germs 
which cause typhoid. These germs have their 
toxins still in their dead bodies and immediately 
cause the blood to manufacture antibodies to 
fight the poisons thus introduced. 

After three inoculations, each containing from 
500,000,000 to 1,000,000,000 or more dead germs, the body 
obtains enough of the resistant antibodies to become immune 



■Wo ATitJtow. Antitoirir-' 

-U5€<3L OA^ used.-or>-> 

•iOOcoot*-' J^ coSc* 



Jr 



J^ealK» 



Typhoid anti- 
toxin has greatly 
reduced the death 
rate from typhoid. 



PUBLIC CONTROL OF DISEASE 423 

fco typhoid. Similar treatment is also used for boils, colds, and 
influenza. 

Immunity which is gained by the blood being stimulated 
to form antibodies which fight the bacteria or their poisons is 
known as active immunity. Examples of such immunity are seen 
in the treatment of smallpox or typhoid. 

Public Control of Disease. — Not only do we have city health 
departments but state- and nation-wide agencies are at work also. 
State departments of health are active in twenty-six states. The 
Federal PubHc Health Service now exercises interstate control of 
communicable diseases — malaria, meningitis, hookworm, and the 
like. In addition to this the Rockefeller Institute is inves- 
tigating the harm hookworm is doing all over the world. It 
has been found that 75 per cent of the inhabitants of Southern 
China, from 60 to 80 per cent of the 300,000,000 inhabitants 
of India, and practically all of the laborers of some South Ameri- 
can tropical regions are infested with hookworms. Since this 
tiny organism not only reduces the working ability of a per- 
son, but also makes him much more liable to other diseases, 
especially tuberculosis, it can be seen that if the disease ia 
stamped out the world will be much better off. This is not 
a difficult task if all cooperate, for the hookworms can be forced 
out of the body by means of thymol and Epsom salts. 

Many other diseases, such as tuberculosis, bubonic plague, 
typhoid, and smallpox, will eventually be practically wiped out 
of existence by medical knowledge, and helpful cooperation of 
rich and poor ahke. 

Summary. — Examples of what private and public control 
of diseases may do are seen when we consider the specific case 
of the disease known as smallpox. In the eighteenth century 
5,000,000 people are said to have died from it; one hundred 
years ago it was exceedingly common in all large cities in this 
country. To-day an epidemic of smallpox is impossible, thanks 
to the discovery of vaccination and prompt action by the 
health departments. Tuberculosis at the present time kills 
more people annually than any other disease, and yet it is be- 
lieved that by sanitary Hving we shall stamp out the disease 
within fifty years if we go on at the present rate. Public 



424 



HEALTH AND DISEASE 



400 



300 



200 



100 



^^— 



hygiene is largely responsible for the lessening of deaths from 
typhoid fever and other diseases whi(;li aie transmitted through 
the milk and water supplies. It is estimated that pure milk, 

pure water, and pure 
air supplied to all would 
lengthen the average hu- 
man life in the United 
States eight years. In 
this country and in parts 
of Europe where sanita- 
tion and hygiene are 
practiced, the life of 
human beings is gradu- 
ally being lengthened. 
In India, on the other 
1850 I860 1870 1880 1890 1900 1914 mo hand, where little hy- 

The curve showing a decreasing death rate giene IS knOWn Or prac- 
from tuberculosis. Why do fewer people die ^{qq^ among the maSSeS 
from the disease than formerly? 1,11 ,i <• 

of people, the length 01 
life is not being increased. Theodore Roosevelt said in one of 
his last messages to Congress : — 

" There are about 3,000,000 people seriously ill in the United States, of 
whom 500,000 are consumptives. More than half of this illness is prevent- 
able. If we count the value of each life lost at only $1700 and reckon the 
average earning lost by iUness at $700 a year for grown men, we find that 
the econonu'c gain from mitigation of preventable disease in the United 
States would exceed $1,500,000,000 a year. This gain can be had through 
medical investigation and practice, school and factory hygiene, restriction 
of labor by women and children, the education of the people in both pub- 
lic and private hygiene, and through improving the efficiency of our health 
service, municipal, state, and national." 

Problem Questions. — 1. What is the value of public health 
agencies in a conmiunit}^? 

2. How does water affect health? Milk? Foods? 

3. How may typhoid be spread? tuberculosis? 

4. What is immunity? How may it be obtained for ty- 
phoid? smallpox? diphtheria? 

5. What pubhc agencies control disease? 



HEALTH AND DISEASE 



425 



6. What is the hookworm disease and how may it be fought ? 
(See pages 200-201.) 

Problem and Peoject References 

Allen, Civics and Health. Ginn and Company. 

Broadhurst, Home and Community Hygiene. J. B. Lippincott Company. 

Davison, The Human Body and Health. American Book Company. 

Gulick, The Efficient Life. Doubleday, Page and Company. 

Gulick, Town and City. Ginn and Company. 

Hough and Sedgwick, The Human Mechanism. Ginn and Company. 

Hunter, Laboratory Problems in Civic Biology. American Book Company. 

Lee, Health and Disease. Little, Brown and Company. 

Richman and Wallach, Good Citizenship. American Book Company. 

Ritchie, Primer of Sanitation. World Book Company. 

Sharpe, A Laboratory Manual. American Book Company. 

Wood, Sanitation Practically Applied. Wiley. 

Zinsser, Infection and Resistance. The Macmillan Company. 




Part of the supply of pure water for the city of New York; the CrotOQ 

Dam and Spillway. 



HUNT. NEW E8. — 28 



GLOSSARY OF SCIENTIFIC TERMS 

(Generic and specific names are not included) 



Abdo'men (Lat. abdomen, belly) : the third region of the body of an in- 
sect; the region of the body below the chest in man. 
Absorp'tion (Lat. ahsorbere, to swallow down): the process of taking up 

food or other substances by chemical or molecular action from the 

digestive tract or elsewhere. 
Adapta'tion (Lat. adaptare, to fit): fitness for surroundings; fitness to do 

a certain kind of work; changes which a plant or animal has undergone 

that fit it for the conditions in which it fives, 
Ad'enoids: fleshy growths in the back of the nose cavity which clog the 

air passages. 
Adul'terant: a substance put in another to cheapen it; usually reducing 

its strength or otherwise injuring it. 
Aero'bic organisms: bacteria or other organisms which require free oxygen 

as opposed to anaerobic organisms (bacteria and some parasitic worms) 

which do not require free oxygen. 
Arcohol: a narcotic poison. 
Al'ga (pi. Algae) : a low form of plant containing chlorophyll. Its body is 

usually a thallus. 
Altema'tion of generations: the alternating of a sexual ^dth an asexual 

phase in the fife-history of a plant or animal. 
Anten'na (pi. Antennae) (Lat. antenna, a sailyard) : a jointed feeler on 

the head of an insect or crustacean. 
Anten'nules : smaU antennse, or feelers. 
Ante'rior (Lat. anterior, former): nearer the head end (Zo5l.); facing 

outward from the axis (Bot.). 
An'ther (Gr. aniheros, flowery) : the part of the stamen which develops and 

contains pollen. 
An'tibodies: substances found in the blood which fight against bacteria 

or prevent them from harming the body. 
Antisep'tic (Gr. anti, against; sepsis, putrefaction): a substance which 

prevents the growth of harmful microorganisms. 
A'nus (Lat.) the posterior opening of the food tube. 
Aor'ta (Gr. aorte, from aeirein, to lift): the large artery leaving the left 

ventricle of the heart. 
Append' age: a jointed organ attached to the side of the body. 

427 



428 GLOSSARY 

Ar'tery (Lat. arieria, windpipe, artery): a tube which conveys blood 

from the heart. 
Asep'tic (Gr. a, not; sepHkos, putrid): free from pus-forming bacteria or 

other harmful organisms. 
Asex'ual: having no sex. 
Assimila'tion (Lat. assimilare, to make like): the conversion of digested 

food into living matter. 
Astig'matism (Gr. a, without; s%ma, spot): a defect of the eye, caused by 

an irregularity in the curvature of the lens. It results in indistinctness 

of vision. 
Au'ricles (Lat. auricula, httle ear) : chambers which receive blood when it 

enters the heart. 
Autonom'ic nervous system (Gr. autos, self; nemos, province): a part of 

the nervous system not under control of the will; the sympathetic 

nervous system. 

B 

Bacil'lus: a rod-shaped bacterium. 

Bacte'ria (Gr. bakterion, a little staff): microscopic one-celled plants, some 

of which cause specific diseases. 
Bacteriology: a study of bacteria. 
Bile: a fluid secreted by the liver. 
Biorogy (Gr. bios, life; logos, discourse): the study of matter in a living 

state, the study of plants and animals. 
Blade: the flat portion of a leaf. 
Blas'tula (Gr. blastos, a bud): a stage in the segmentation of an egg in 

which the cells form a hollow ball with a wall one layer thick. 
Bud: an undeveloped branch. 



Cal'orie (Large calorie) (Lat. calere, to be warm) : a heat unit, namely, the 

amount of heat required to raise the temperature of one kilogram of 

water one degree Centigrade. 
Calorim'eter : a machine for measuring heat units. 
Cam'bium: the growing layer of a stem. 
Cap'illaries (Lat. capillus, a hair): minute tubes which connect arteries 

with veins. 
Capillar'ity: a phenomenon shown by liquids rising in fine tubes. 
Car'apace (Sp. carapacho, a covering): a shell-hke covering on the dorsal 

side of some animals, as crustaceans. 
Carbohydrate (Lat. carbo, coal; Gr. hydor, water): a class of nutrients 

composed of carbon, oxygen, and hydrogen, having the oxygen and 

hydrogen in the same proportion as water. 
Car'bon (Lat. carbo, coal): an element found in all organic compounds. 
Carbon dioxide: a gas, a product of the oxidation of carbon. 



GLOSSARY 429 

Cell: the structural and physiological unit in plant and animal bodies. A 

small mass of protoplasm inclosed in a cell membrane and usually 

containing a nucleus. 
Cell membrane: the deUcate Uving covering of a cell. 
Cell sap; water, with materials in solution, found in the vacuoles of plant 

cells. 
Cellulose: a dead substance found in the cell walls of plants. 
Cen'tnim (Lat. centrum, center): the stout body of a vertebra. 
Cephalotho'rax (Gr. kephale, head; thorax, chest): body region in crus- 
taceans formed by the fusion of head and thorax. 
Cerebel'ltmi (Lat., diminutive of cerebrum) : part of the brain between the 

cerebrum and the medulla oblongata. 
Cer'ebnim (Lat. cerebrum, the brain): the anterior part of the brain. 
Chel'ipeds (Gr. chele, claw): pincher claws of arthropods. 
Chemical element: a substance which has never been broken down into 

simpler substances. 
Chi'tin (Gr. chiton, a tmiic): a hard substance present in the exoskeleton 

of insects. 
Chlo'rophyll (Gr. chloros, grass green; phyllon, a leaf): the green coloring 

matter of plants. 
Chlo'roplasts: small bodies of protoplasm which contain chlorophyll. 
Cho'roid: the middle coat of the eye. 
Chro'mosome (Gr. chroma, color; soma, body): a deeply staining body in 

the nucleus of a cell, supposed to carry the determiners of hereditary 

qualities. 
Chrys'alis (Gr. chrysos, gold) : the uncovered pupal stage of butterflies. 
Cil'ium (Lat. cilium, an eyehd with hairs growing on it): a tiny hairhke 

thread of protoplasm extending from a cell. 
Cloa'ca (Lat. cloaca, sewer): the common cavity into which the digestive, 

urinary, and reproductive systems open in some kinds of vertebrates. 
Coc'cus (Gr. kokkus, berry): a ball-shaped bacterium. 
Cocoon': The egg-case of spiders; a silky covering around a pupa. 
Cce'lom (Gr. koilos, hollow): the true body cavity, through which the 

digestive tract passes. 
Compound eye: an eye made up of many simple eyes or ommatidia. 

Arthropods have compound eyes. 
Conjuga'tion (Lat. cum, together with; jugare, to yoke): the temporary 

union of two sex cells of equal size, with a fusion of nuclei and inter- 
change of nuclear material. 
Connective tissue : collections of cells which support and connect other tissues. 
Contrac'tile vac'uole: a small vesicle, found in the cytoplasm of many 

protozoa, which appears and disappears with regularity. It is beHeved 

to be an organ of excretion. 
Cor'puscles (Lat. corpusculum, a Uttle body): the red and colorless cells 

in the blood. 



430 GLOSSARY 

Cor'tex: a fleshy portion of the root, outside the central cylinder. 

Cotyle'don (Gr. kotyledon, socket): the seed leaves. Plants may be 
grouped as monocotyledons, having one seed leaf; dicotyledons, having 
two seed leaves; and polycotyledons, having many seed leaves. 

Cul'ture: a growth of bacteria or other microorganisms in prepared nu- 
trient media. 

Cy'toplasm (Gr. kytos, a vessel; plasma, anything formed): the living 
substance of the cell outside of the nucleus and inside the cell mem- 
brane. 

D 

Dehis'cent fruits (Lat. de, from; hiscere, to open): fruits that spUt open to 

discharge their seeds. 
Deliques'cent tree (Lat. deliquescere, to melt, dissolve) : a spreading tree, as 

the elm. 
Der'mis (Gr. derma, skm): the layer of skin below the epidermis. 
Di'aphragm (Gr. diaph ^nmxi, a partition wall): the muscular partition 

between the thorax and the abdomen. 
Di'astase: an enzyme formed in plants which changes starch to grape 

sugar. 
Dichog'amy (Gr. dicha, in two; gamos, marriage): a condition in which 

the stamens ripen before the pistil or vice versa, thus preventing 

self-pollination. 
Dicotyle'don: a plant that bears seeds having two cotyledons. 
Diges'tion (Lat. digestio, the dissolving of food): the process of preparing 

food for absorption. 
Dimor'phic (Gr. di^, twice; morphea form): flowers which have two forms, 

one having long pistils and short stamens, the other short pistils and 

long stamens. 
Disinfect'ant: something which kills bacteria. 

Dor'sal (Lat. dorsum, the back): of or pertaining to the back or top side. 
Ductless glands: glands which have no communication with an outer 

surface, and which manufacture hormones. 

E 

Ec'toderm (Gr. eclos, outside; derma, skin;: the outer layer of a many- 
celled animal. 

Em'bryo (Gr. emhryon, a young one) : the early stage of a developing plant 
or animal. 

Em'bryo sac: the structure within the ovule which holds the egg cell. 

Emursion (Lat. emulgere, to milk out): a mixture of liquids which do not 
dissolve, the particles of one floating as small globules in the other. 

En'dodenn (Gr. endon, within; derma, skin): the inner layer of cells in 
an embryo, giving rise to the digestive tract, etc. 

En'doskeleton (Gr. endon, within; skeletos, hard): a skeleton inside the 
body as opposed to the outer or exoskeleton. 



GLOSSARY 431 

En'dosperm (Gr. endon, within) : food stored in the seed outside the embryo. 
En'ergy (Gr. energos, at work); work power; ability to perform work. 
Envi'ronment (Fr. environ, about) : the surroundings of an organism. 
Eu^zyme (Gr. en, in; zyme, leaven) : a substance which brings about a 

chemical action, assisting in digestion. 
Epider'mis (Gr. epi, upon; derma, skin): an outer layer of cells; the 

outside skin. 
Ep'iphytes {epi, upon; Gr. phyton, plant) : air plants and tropical plants that 

obtain moisture from the atmosphere. 
Ero'sion (Lat. erodere, to gnaw off) : the wearing away of rocks through 

the agency of water, wind, glaciers, and other agencies. 
Essen'tial organs: the stamens and pistils, parts of a flower which have 

to do with the production of seeds. 
Eusta'chian tube: the canal connecting the tympanic cavity with the 

pharynx, named for its discoverer, Eustachio, an Italian physician. 
Excur'rent tree (Lat. ex, out; currere, to run): a tall slender tree with 

one main trunk, as the cedar. 
Exoskereton: an outside skeleton. 



Fatigue' (Lat. fatigare, to weary) : the effect produced by long stimulation 

on the cells of an organism. 
Fats: a class of nutrients composed of much carbon and hydrogen with a 

little oxygen. 
Fermenta'tion (Lat. fermenium, ferment): the chemical transformation of 

organic substances through the agency of enzymes or ferments, or 

through the agency of bacteria. 
Fertiliza'tion (Lat. fertilis, fruitful) : the union of an egg cell and a sperm 

cell. 
Fibrovas'cular bundles: collections of tubular cells, supported by woody 

cells, which conduct fluids in plants. 
Fin: a fold of skin, with skeletal supports, used for swimming. 
Fis'sion (Lat. fissum, cleft) : division of a cell into two parts. 
Flagel'lum (Lat. fiagellum, whip) : a vibratory threadlike projection of 

certain cells. 
Food: a substance that forms the material for the growth or repair of the 

body of a plant or an animal or that furnishes energy for it. 
Fruit: a ripened ovary together with any parts of the flower adhering to it. 
Func'tion (Lat. functio, performance): the normal action of an organ or 

organs. 

G 

Game'tophyte (Gr. gamete, wife): the phase in the life history of a thallus 

plant that produces the sex organs, 
Gan'glion (pi. Ganglia ) (Gr. ganglion, little tumor) : a mass of nervous 

matter containing nerve cells which give rise to fibers. 



432 GLOSSARY 

Gas'tric glands (Gr. gaster, stomach): digestive glands found in the walls 
of the stomach, 

Gas'trula (Gr. gaster, stomach): a cuphke structure formed by the in- 
vagination or turning in of the blastula. 

Geot'ropism (Gr, ge, earth; tropein, to turn) : response to gravity. 

Germina'tion : the beginning of growth in a seed or pollen grain. 

Gill rakers : small spinehke structures attached to gill arches which prevent 
escape of food. 

Gills: breathing organs for use in water. 

Gland (Lat. glans, an acorn): an organ which secretes material to be used 
in or excreted from the body. 

Gly'cogen (Gr. glykus, sweet; -gen, producing): animal starch, found in 
the liver. 

Guard cells: epidermal cells, found on each side of a stoma. 

Guriet (Lat. gula, gullet): a muscular canal extending from the mouth 
cavity to the stomach. 

H 

Haemoglo'bin (Gr. haima, blood; globos, sphere): red coloring matter of 

the blood. 
Hair follicle (Lat. folliculus, a Httle bag): a little pit in the skin from 

which a hair grows. 
Harophjrte (Gr. hals, salt) : a plant which grows best in salty soils. 
Heliot'ropism (Gr. helios, sun; tropein, to turn) : response to light. 
Hered'ity (Lat. heres, heir) : transmission of quahties from parent to child. 
Hermaphroditic (Gr. hermaphroditos, combining both sexes): an organism 

having both male and female sex organs, 
Hi'lum: a scar on the testa left where the seed was attached to the pod. 
Hor'mones (Gr. hormaein, to excite) : substances from the organs of the 

body which effect a chemical coordination. 
Hu'mus (Lat. humus, ground): vegetable mold, a black or dark colored 

substance formed by the decay of organic substances in the soil. 
Hy'brid (Lat. hyhrida, mongrel): the offspring of parents of two different 

species or varieties. 
Hy'drophyte (Gr. hydor, water): a water-loving plant. 
Hy'giene (Gr. hygeia, health): a study of the preservation of health. 
Hypocot'yl (Gr. hypo, under): the part of the developing embryo which 

forms the root and the lower part of the stem. 



Immu'nity (Lat. immunis, free from duty): the successful resistance of an 

organism to infections from microorganisms. 
Imperfect flowers: flowers having only one kind of essential organs, either 

stamens or pistils. 
tntes'tine (Lat. intestinus, internal) : the food tube in vertebrates from the 



GLOSSARY 433 

pyloric end of the stomach to the anus. It is divided into the small 

and the large intestine. 
InVolucre (Lat. involucrum, a wrapper): a whorl of leafiike bracts around 

the base of a flower cluster. 
I'ris (Gr. iris, rainbow): the colored portion of the eye, having the pupil 

in the center. 

K 

Kad'neys: glands which secrete urine. 

Elinet'ic (Gr. hinein, to move): energy employed in producing motion. 



Lac'teals (Lat. lacteus, milky): lymphatic vessels which carry fats and 

other substances from the intestine to the thoracic duct. 
Lar'va (Lat. larva, a ghost) : an embryo which becomes self-sustaining but 

which does not have the characteristics of the adult. 
La'tent (Lat. latere, to lie hid) : lying dormant but capable of development. 
Leg'umes (Lat. legere, to gather): plants which bear seeds in pods — peas, 

beans, and the like; also the seeds of such plants. 
Len'ticel: a breathing hole in the bark. 
Lig'ament (Lat. Ugare, to bind): a band of connective tissue binding one 

bone to another. 
Liv'er: a digestive gland which secretes bUe. 
Lymph (Lat. lympha, water): plasma and colorless corpuscles outside of 

the blood vessels. 

M 

Macronu'cleus (Gr. makros, large): the large nucleus, as opposed to 

the micronucleus, or small nucleus. 
Mam'mary glands (Lat. mamma, breast): milk-secreting glands found in 

mammals. 
Man'dible (Lat. mandere, to chew) : in insects, a hard cutting jaw. 
Man'tle (Lat. mantellum, a cloak) : the soft outer fold of skin in moUusks 

which secretes the outer shell. 
Maxil'la (Lat. maxilla, a jaw) : an appendage near the mouth of arthropods, 

modified in insects to form an organ for getting food. 
Maxil'liped (Lat. mxixilla, jaw; pes, foot): an appendage next posterior 

to the maxilla in arthropods. Foot jaw. 
Medul'la oblonga'ta (Lat. medulla, pith): the most posterior part of the 

brain. 
Med'ullary rays (Lat. medulla, pith) : thin plates of pith which separate the 

wood of dicotyledonous stems into wedge-shaped masses. 
Mes'oderm (Gr. mesos, middle; derma, skin): the middle layer of cells 

in a young animal embryo. 
Mes'ophjrte (Gr. mesos, middle): a plant preferring moderate conditions 

of moisture. 



434 GLOSSARY 

Metamor'phosis (Gr. meta, after; rnorphe, form): change of form undergone 

from egg to adult, as in insects. 
Metazo'a (Gr. meta, after; zoon, animal): animals having many cells in 

the body. 
Mic'ropyle (Gr. micropyle, a Httle gate): the hole where the pollen tube 

enters the embryo sac. 
Mid 'rib: central vein of a leaf. 
Mi'grant: an animal which moves from one place to another and back 

regularly at stated seasons of the year. Many birds migrate to warmer 

regions for the winter. 
Mim'icry (Gr. mimikos, imitative): the imitation in form or color of a 

harmful insect by a harmless one which is protected thereby. 
Monocotyle'don: a plant that bears seeds having but one cotyledon. 
Mo'tor (Lat. movers, to move): connected with movement. 
Mu'cous membrane (Lat. mucus, slime; membrana, skin): a delicate moist 

membrane lining all body passages which have an external opening. 
Mus'cle (Lat. musculus, muscle): a contractile tissue capable of bringing 

about movement. 
Muta'tion: a heritable modification arising from internal causes in an 

organism. 
Mycelium: the threadlike body of a mold, the individual threads being 

called hyphae. 

N 

Narcotic (Gr. narkotikos, making dumb): a substance which blunts the 

senses and in large quantities causes insensibility. 
Nec'tar (Gr. nectar, drink of the gods): a sweet fluid secreted by certain 

groups of cells known as nectar glands in a flower. From this substance 

bees make honey. 
Nic'titating membrane (Lat. nictare, to wink): the third eyelid, a delicate 

membrane covering the eye in birds and frogs. 
Ki'trogen (Lat. nitrum, natron; -gen, producing): a gaseous element, 

found in many organic compounds and forming almost four fifths 

of the atmosphere. 
Nu'cleus (Lat. nucleus, a kernel): the center of activity in the cell. 



Ommatid'ium (Gr. omm/i, eye): one of the elements of a compound eye. 
Oper'culum (Lat. operculum, a Hd): a lid or flap in fishes, covering the 

gills. 
Op'sonin (Gr. opsonein, to cater for) : a substance in the blood which helps 

colorless corpuscles destroy bacteria. 
Or'ganism (Gr. organon, an instrument): a body which is made up of 

organs or parts, each of which has a special function; any animal or 

plant. 



GLOSSARY 435 

Osmo'sis: diffusion of dissolved substances through a semi-permeable 
membrane, the greater flow being toward the denser medium. 

O'vary (Lat. ovum, egg) : the base of a pistil, containing the ovules. 

Ovipos'itor (Lat. ovum, egg; ponere, to place): a specialized structure 
for depositing eggs, foimd in insects. 

Oxida'tion: the chemical union of oxygen with some other substance. 

Ox'ygen (Gr. oxvs, acid; -gen, producing): a gaseous element found in 
the air and in many compounds. 



Pal'ate (Lat. palatum): the roof of the mouth. The hard palate is sup- 
ported by bone; the soft palate is a fold of mucous membrane lying 
posterior to the hard palate. 

Pal'pus or palp (Lat. palpare, to touch) : in arthropods, an appendage at- 
tached to a mouth part; usually an organ of touch or taste. 

Pan'creas (Gr. pan, all; kreas, flesh): a digestive gland which secretes 
pancreatic juice. 

Pap'pus: a downy or flufty outgrowth from the ovary wall. 

Par'asite: an organism which secures its hving directly from another 
hving organism without giving anything in return. 

Pas'teurize (from Pasteur the scientist, p. 3) : to heat milk to about 160° 
Fahrenheit for about 20 minutes for the purpose of killing bacteria in it. 

Pec'toral girdle (Lat. pectoralis, pertaining to the breast): bones which 
support the anterior pair of appendages in vertebrates. 

Pel'vic girdle (Lat. pelvis, a basin): the bony arch to which the posterior 
pair of appendages are attached in vertebrates. 

Pet'al: one of the leaflike parts of the corolla. 

Pet'iole (Lat. petiolu^, sl Httle foot): the stalk of a leaf. 

Phag'ocjrte (Gr. phagein, to eat; kytos, cell): a colorless corpuscle which 
destroys bacteria. 

Phar'ynx (Gr. pharynx, gullet) : an irregular cavity at the back of the mouth. 

Phlo'em (Gr. phloos, bark): the outer part of a fibro vascular bundle con- 
taining the sieve tubes. 

Photosyn'thesis (Gr. phos, hght; synthesis, a putting together): the proc- 
ess of making starch out of carbon dioxide and water by the aid of 
sunlight, as done by a green cell. 

Physiolog''ical division of labor: performance of different kinds of work 
by different parts of an organism. 

Physiorogy (Gr. physis, nature; logos, discourse): study of the fimctions 
of plants and animals. 

Pis'til: a structure in the flower containing the ovary, in which the seeds 
are formed. 

Pith: the soft, spongy center of a dicotyledonous stem. 

Plas'ma (Gr. plasma, anything formed or molded): the colorless fluid 
part of blood. 



436 GLOSSARY 

Pleu'ra (Gr. pleura, the side) : the membrane which covers the lungs and 

lines the cavity containing them. 
Plu'mule: the part of the embryo above the cotyledons which develops 

into the stem and leaves. 
Pol'len grain: a structure in flowers which contains the sperm cell or 

male gamete. 
Pollina'tion: the transfer of pollen from the anther to the stigma. Self- 
pollination is transfer between parts in the same flower ; cros^-pollination 

is transfer between different flowers, or, some say, between flowers on 

different plants. 
Polycotyle'don: a plant that bears seeds having several cotyledons. 
Poryp (Lat. -poly-pus, a polyp): a simple actinozoan, as a sea anemone or 

a single coral individual. 
Poste'rior (Lat^. posterior, later): behind, last, or tail end of an animal. 
Pri'mates: the highest order of mammals, including the monkeys, the apes, 

and man. 
Probos'cis (Gr. pro, before; boskein, to feed) : a slender sucking tube found 

in insects. 
Proglot'tids (Gr. pro, forward; glotta, tongue) : reproductive body segments 

of a tapeworm. 
Pro 'leg: an unjointed abdominal appendage of insect larvae. 
Prosto'mium: a projecting part of upper hp of the earthworm. 
Protec'tive resemblance: the hkeness of hvdng organisms in color or form 

to their immediate surroundings, thus securing protection from attack 

of enemies. 
Pro'teins (Gr. protos, first): nitrogenous compounds found in the bodies 

of plants and animals; a class of nutrients composed of nitrogen, car- 
bon, hydrogen, and oxygen, together with other elements in some cases. 
Pro'toplasm (Gr. protos, first; Lat. plasma, a thing formed): the hving 

substance of plants and animals. 
Protozo'a (Gr. protos, first; zoo7i, animal): one-celled animals. 
Pseudopo'dium (Gr. pseudes, false; pov^, foot): a projection of protoplasm 

used for locomotion in protozoa. 
Pto'maine (Gr. ptoma, a corpse): poisonous alkaloidal material probably 

the result of decomposition of organic matter. 
Pu'pa (Lat. pupa, puppet): the quiescent stage in insect development 

preceding the adult. 
Pylo'rus (Gr. pyloros, gatekeeper): the opening of the stomach into the 

intestine. 

Q 

Quar'antine (Fr. quarante, forty): isolation of the sick to prevent spread 
of infectious disease. 

R 

Ray flowers: modified flowers at the outer edge of a flower cluster such 
as a composite head. 



GLOSSARY 437 

Regenera'tion (Lat. re, again; generare, to beget): the growing again of 

a part of an animal which has been lost. 
Respira'tion (Lat. re, again; spirare, to breathe): taking in of oxygen and 

giving out of carbon dioxide by Kving cells. 
Ret'ina (Lat. rete, a net): the coat of the eye in which the optic nerve 

fibers terminate. 



Sali'va (Lat. saliva, spittle): the secretion of the salivary glands. 
Sap'rophyte (Gr. sapros, rotten; phyton, plant): an organism which derives 

its nourishment from dead organic matter, as a mold or mushroom. 
Sclerot'ic coat (Gr. skleros, hard): the outer coat of the eye. 
Scute (Lat. scutum, a shield): an external scale, as in the snake. 
Seed: a structure formed in a fruit as a result of the fertilization of the 

egg cell. 
Seg'ment (Lat. segmentum, a piece cut off): one of a number of serial 

divisions of an animal's body or of an organ. 
Sen'sory (Lat. sensu^, feehng): having direct connection with any part of 

the seat of sensation. 
Se'pal: a leaflike part of the calyx or outer circle of parts in a flower. 
Se'tae (Lat. seta, a bristle): bristles, used for locomotion in earthworms 

and other animals. 
Sex'ual (Lat. sexus, sex): pertaining to or having sex. 
Si'phon (Gr. siphon, a tube) : a "tube through which water may pass into 

and out from the mantle cavity of a mollusk. 
Spe'cies: the smallest group of organisms having characteristics in common 

that make them different from all other organisms. 
Sperm cell: the male sex cell or gamete. 

Spi'nal cord: a cord of nervous tissue lying in the vertebral column. 
Spir'acles (Lat. spiraculum, breathing hole): breathing holes in insects. 
Spirillmn (Lat. spira, coil): a spiral form of bacteria. 
Spongy paren'chyma (Gr. para, beside; en, in; chein, to pour): a layer 

of loosely placed cells forming a tissue in the leaf. 
Sporan'gium (Gr. sporos, a seed; aggeion, a vessel) : a sac containing spores. 
Spore: a reproductive cell capable of growing into a mature organism. 
Spo'rophyte: spore-bearing part of a plant. 
Sta'men: an organ of the flower in which pollen is formed. 
Ster'ilize (Lat. sterilis, barren): to destroy bacteria and other organisms, 

usually by heating. 
Stig'ma (Gr. stigma, the prick of a pointed instrument) : the part of a pistil 

which receives the pollen grains. 
Stim'ulant (Lat. stimulus, a goad): a substance which causes temporary 

activity of nerve or muscle. 
Stim'ulus (Lat. stimulare, to incite): an agent which causes an organism 

or some part of it to react when affected by it. 



438 GLOSSARY 

Stip'ule (Lat. stipida, stem): a leaflike outgrowth at the base of the 

petiole. 
Sto'ma (pi. Sto'mata) (Gr. stoina, a mouth): a breathing hole in a leaf. 
Stom'ach (Gr. stomachos, throat): a sac-like part of the food tube between 

gullet and intestine. 
Sweat glands: excretory glands in the skin. 

Swim'merets: paired appendages on the abdomen of crustaceans. 
Symbio'sis (Gr. symbio>iis, a living together): a condition in which two 

organisms of different kinds hve together in a mutually beneficial 

partnership. 



Tac'tile corpuscle (Lat. fati'gcrc, to touch): sense organ of touch. 

Tar'sus (Gr. tarsos, sole of foot): the ankle-bones, also the last region of 

the leg of an insect. 
Taste bud: end organ of taste found on the tongue. 

Teeth: limy structures in the mouth of man and other animals, consist- 
ing of incisors or cutting teeth; canines, tearing teeth; and molars 

and premolars, crushing and grinding teeth, 
Ten'don (Lat. tendere, to stretch): a band of connective tissue attaching 

muscle to muscle or muscle to bone. 
Ten'tacle (Lat. tentacidum, a feeler): a flexible organ at the anterior end of 

an animal used for feehng, grasping, etc. 
Tes'ta: the thick outer coat of a seed. 
Thal'lophytes (Gr. thallos, young shoot; phjjton, plant): plants having a 

thallus or ribbonhke bodj'. 
Thorac'ic: pertaining to the chest region. 
Thorax (Gr. thorax, the chest): the part of the body between the head 

and the abdomen. 
Tissue (Fr. fissu, a web): a collection of cells all more or less alike and 

ha\'ing the same fimction. 
Tra'chea (Lat. trachia, -u-indpipe) : the windpipe; also a respirator}' tube 

of insects. 
Transpira'tion (Lat. traths, through; spirare, to breathe): the gi\'ing off 

of water vapor from plants. 
Trichi'na: pork worm, a parasitic roundworm causing the condition called 

trichinosis. 
Trimor'phic (Gr. tri, three; morphe, form) : flowers ha\'ing three lengths 

of stamens and pistil; for example, the loosestrife. 
Tryp'anosomes (Gr. trypanon, an auger): protozoa which cause diseases 

such as sleeping sickness. 
Tym'panum (Gr. tympanon, a drum): the eardrum. 

U 

U'rea (Lat. urina, urine): a nitrogenous waste excreted in the urine. 



GLOSSARY 439 



Vaccina'tion: inoculation with a vaccine, containing living or dead bac- 
teria, to protect the body from disease. 
Vac'uole (Lat. vacuus, empty): a space in protoplasm containing air, 

water, sap, or food material. 
Varia'tion: in biology, the occurrence of differences between individuals 

of the same species. 
Vein: a tube which conveys blood to the heart. 
Ven'tral (Lat. venter, belly) : the opposite of dorsal. 

Ventila'tion (Lat. ventilare, to air) : changing of air in a room or building. 
Ven'tricle (Lat. ventriculus, a httle beUy): a muscular chamber of the 

heart, which forces the blood out. 
Ver'miform appendix (Lat. vermis, worm): a narrow tube about four 

inches long, closed at the outer end, near the beginning of the large 

intestine of man. 
Ver'tebrse (Lat. vertere, to turn): bones of the vertebral column. 
Ver'tebrate: an animal ha\dng a backbone. 
Vil'lus (Lat. villus, shaggy hair): a minute projection, an absorbing organ 

of the small intestine. 
Vi'rus: an unknown agent causing disease, as opposed to bacteria or 

protozoa which are known causes of specific diseases. 
Vi'tamin (Lat. vitay life) : unknown substances in food apparently necessary 

to support life. 
Vcruntary (Lat. voluntas, will): subject to the will (used with reference 

to muscles), as opposed to involuntary. 

X 

Xe'rophyte (Gt. xeros, dry): a plant which lives under conditions of 

extreme dryness. 
Xy'lem (Gr. xylon, wood): the inner woody part of a fibrovascular bundle 

which conducts water up the stem 



INDEX 



(Illustrations are indicated by page numerals in bold-faced type.) 



Accommodation of eye, 399. 
Acts, automatic, 393. 
Adaptation, 19, 30, 204. ^ 
Adaptations, for pollination, 35, 36; 

for respiration, 375; 

for seed dispersal, 42, 43, 44, 45, 
46; 

in birds, 286, 288, 290, 291; 

in frogs, 272; 

in mammalia, 303; 

in snakes, 284; 

in turtles, 281; 

in vertebral column, 318; 

to environment, 126, 234. 
Adenoids, effects of, 382. 
Agglutinins, 358. 
Aggressive resemblance, 235. 
Air, amount of, in breathing, 377; 

changed in lungs, 378; 

composition of, 6, 7; 

factor in germination, 62; 

fresh, how to get, 405; 

in hygiene, 410; 

necessity of, 395; 

value of change of, 406. 
Alcohol, and ability to do work, 401 ; 

and disease, 408; 

and longevity, 409; 

a poison, 337; 

as a food, 336, 338; 

effect on blood, 372; 

effect on body heat, 387; 

effect on circulation, 373; 

effect on digestion, 356; 

effect on intellectual ability, 401; 

effect on respiration, 388; 

in patent medicines, 340; 

in treatment of disease, 408; 

paralyzes nervous system, 401. 
llcoholic poisoning, economic, moral 
and social effects of, 402. 

HUNT. NSW £8. — 29 



Algae, 127. 

AUmentary canal, 343. 
Alligator, 284. 

Alternation of generations, in coelen- 
terates, 191; 

in fern, 132; 

in mosses, 131; 

in spermatophytes, 133. 
Amino-acids, 349, 351. 
Amoeba, parts of, 175; 

reproduction of, 176. 
Amphibia, 272; 

characteristics of, 280; 

classification of, 280. 
Angiosperms, 134. 
Animals, cold-blooded, 362; 

domestication of, 308; 

relation of, to man, 3; 

vertebrate, 260. 
Annulata, classification of, 202. 
Antennae, 206. 
Antennules, 206. 
Anther, 25. 
Antiseptics, 163. 
Antitoxin, 421, 422. 
Ants, 240; 

and their "cows," 241. 
Anvil, 397. 
Aphids, 228; 

and ants, 241. 
Appendages of skeleton, 319. 
Aptera, 232. 

Aqueous humor, 398, 399. 
Arachnida, 232. 
Arteries, 362; 

structure of, 366, 367. 
Arthropoda, classified, 231. 
Asexual reproduction, amceba, 17^ 

coelenterates, 191, 192; 

in fern, 132; 

in hydra, 184; 



441 



442 



INDEX 



Asexual reproduction, in mold, 150; 

in moss, 131; 

in Paramecium, 174; 

in spirogyra, 129. 
Astigmatism, 399. 
Atoll, 192. 
Auricle, 363. 

Bacillus, 154. 
Bacteria, 153; 

and fermentation, 158; 

carried by fly, 225, 406; 

cause decay, 157; 

cause disease, 159; 

conditions for growth, 156; 

discovery of, 154; 

from human mouth, 158; 

in impure water, 417; 

in milk, 159; 

LQ school room, 380; 

in streets, 405; 

method of study, 155; 

nitrogen-fixing, 167, 158; 

size and form, 154; 

their relation to man, 2. 
Bacteriology, defined, 3. 
Balanced aquarium, 166. 
Balancing in birds, 289. 
Banana plants, 2. 
Bark, use of, 87. 
Barley, production of, 49. 
Bean, 54. 

Beans, as food, 56. 
Beaver, 305. 
Bees, 30, 32, 238. 
Beetle, characteristics of, 226. 
Berry, 42, 52. 
Beverages, 53. 
Bile, functions of, 351. 
Bile duct, 343. 
Biology, 1; 

civic, 415; 

its relation to society, 5; 

reasons for study of, 1. 
Birds, body of, 286; 

care of young, 293; 

classification of, 301; 

distribution of, 293; 

economic importance of, 294; 

extermination of, 300; 



Birds, feathers of, 287; 

feet of, 288; 

harmful to man, 300; 

migrations of, 293; 

nesting habits of, 292, 293; 

perching in, 289; 

wings of, 286. 
Bison, 306. 
Bladder, urinary, 384. 
Blastula, 182. 
Blood, amount of, 362; 

and its circulation, 358; 

changes in, in body, 386: 

changes in, in lungs, 375, 378; 

clotting of, 359; 

course of, 364, 365; 

disease-resisting mechanism of. 
361; 

distribution of, 362; 

effec^: of alcohol on, 372 ; 

exchs.nge in, 369; 

function of, 358; 

tempei'ature of, 362; 
. vessels, congestion in, 388; 

wastes of, to kidney, 384. 
Bluebird, 295. 
Body, daily fuel needs of, 331 ; 

normal heat output of, 332. 
Bodv heat, affected bv alcohol, 

387; 

in cold-blooded animals, 386; 

regulation of, 385. 
Box elder, section of, 86. 
Brain, functions of parts, 392; 

of man, 391. 
Bread mold, 150. 
Breathing, and tight clothing, 381: 

hygienic habits of, 381; 

mechanics of, 376; 

movements in, 376: 

rate of, 377. 
Bronchi, 374. 

Bruises, treatment of, 371. 
Bryophjiies, 134. 
Budding, 93, 94. 
Bugs, 227, 228. 
Bumblebee, 30, 238. 
Burbank, Luther, 68. 
Burns, treatment of, 387. 
Butter and eggs, 33. 



INDEX 



443 



Butterfly, 221; compared with moth, 
222, 223; 
head of, 221. 

Caffeine, 336. 

Calorie, defined, 326. 

Calyx, 24. 

Cambium layer, use of, 87, 94. 

Canal, semicircular, 397, 398. 

Capillaries, 362. 

Capillarity, 76. 

Capillary circulation in frog's foot, 

366. 
Carapace, 205. 
Carbohydrates, 13, 323. 
Carbon, properties of, 10. 
Carbon dioxide, test for, 11. 
Carnivora, 303. 
Catarrh, 382. 
Catbird, 298. 
Cell, 20; 

as a unit, 177. 
Cell membrane, 20, 74, 75. 
Cell sap, 74, 75. 
CeU wall, 74. 
Cells, 187. 

in tissues of man, 187; 

nerve, 391; 

sizes and shapes of, 21. 
Centipedes, 231. 
Centrum, 318. 
Cephalopods, 257, 259. 
Cephalothorax, 205. 
Cerebellum, 391. 
Cerebrum, 391; 

functions of, 392. 
Cestodes, 199. 
Chelipeds, 205, 206. 
Chemical element and compound, 7. 
Chickadee, 296. 
Chitin, 217. 
Chlorophyll bands, 129; 

bodies in leaf, 104. 
Chromosomes, 20. 
ChrysaUs, 222, 223. 
Cicada, 227, 228. 
Ciha, 154, 173. 
Circulation, effect of alcohol on, 372; 

effect of exercise on, 371; 

in a mammal, 365; 



Circulation, in capillaries, 366, 367; 

in crayfish, 208; 

in fishes, 264; 

in frog, 275, 366; 

in kidney, 384; 

in man, 362; 

organs of, 188; 

portal, 354, 365; 

pulmonary, 364, 365; 

systemic, 364, 365. 
Clam, fresh-water, shell of, 254; 

round, parts of, 255. 
Class, defined, 134. 
Coccus, 154. 
Cochlea, 397, 398. 
Coelenterates, 189, 190, 191, 192* 

compared with worms, 197. 
Colds, care of, 387; 

cause of, 387. 
Coleoptera, 226, 232. 
Combustion, 11. 
Composite head, parts of, 34, 
Condiments, 53. 
Conjugation, 130, 150; 

in mold, 150; 

in Paramecium, 174. 
Coral, 191; 

madreporic, 192. 
Coral reefs, 192. 
Corn, ear of, 56; 

grain of, 56, 57; 

production of, 48; 

uses of, 48. 
Corn grain, foods in, 57, 59. 
Cornea, 398. 
Corolla, 24. 

Corpuscle, colorless, functions of 
361; 

structure of, 359, 360. 
Corpuscle, red, function of, 359; 

structure of, 359. 
Corpuscles, tactile, 313, 39& 
Cortex, 73; 

in stem, 86. 
Cotton, fumigation of, 51; 

production of, 50, 51; 

uses of, 51. 
Cotton boll weevil, 51, 246. 
Cotyledons, food in, 55; 

functions of, 64; 



Ui 



INDEX 



Cotyledons, in bean, 54, 55; 

of corn, 57. 
Crab, blue, 212; 

fiddler, 213; 

giant spider, 213; 

hermit, 212. 
Crayfish, adaptation for protection, 
205; 

and aUies, characteristic of, 214; 

appendages, 207; 

external structure, 205; 

internal structure, 208; 

locomotion of. 205; 

senses of, 206. 
Cretinism, 368. 
Crocodiles, 284. 
Crops, rotation of, 80. 
Cross-pollination, defined, 27. 
Crow, 299. 
Crustaceans, 205; 

habitat of, 214. 
Culture, pure, 155. 
Cuts, treatment of, 371, 387. 
Cytoplasm, 20. 

DandeUon, 72. 

Decay by bacteria, 157. 

Deer, Virginia, 306. 

Dehquescent tree, 84. 

Dermis, 313. 

Development of bee, 238, 239; 

of crayfish, 209; 

of fly, 225; 

of frog, 276, 277, 278; 

of lobster, 210, 211; 

of moth, 223. 
Diaphragm, 348; 

in respiration, 376. 
Diastase, action of, on starch, 58. 
Diatoms, 129. 
Dichogamy, 35. 
Dicotyledons, 59, 60 
Diet, best, 326. 
Diffusion, 75. 
Digestion, 343; 

and absorption, 343; 

effect of alcohol on, 356; 

in corn grain, 58; 

in crayfish, 209; 

in fishes, 264; 



Digestion, in plants, 89; 

of starch, 347; 

organs of, 188, 343; 

purpose of, 343. 
Digestive tract in frog, 274, 275 
Dipnoi, 271. 
Diptera, 224, 226, 232. 
Disease, prevention of, 404. 

pubHc control of, 423. 
Diseases, carried by food, 420; 

caused by bacteria, 159, 162; 

due to insects, 243, 244; 

infectious, 421; 

of nose and throat, 382. 
Disinfection, 421. 
Division of labor, 181; 

in honeybee, 239; 

in hydra, 186; 

in vorticella, 177. 
Dragon fly, 228, 229, 
Drone, 238. 

Drugs, use and abuse of, 340. 
Drupe, 52. 
Dusting, 380. • 

Dyspepsia, causes and prevention 
of, 355. 

Ear, human, 397. 

Earthworm, development of, 197; 

locomotion of, 196 ; 

relation to surroundings, 194. 
Eating, hygienic habits of, 355. 
Economic importance^ of alcoholic 
poisoning, 402; 

of birds, 294; 

of carnivora, 304; 

of corals, 192; 

of earthworms, 197; 

of ferns, 132; 

of fish, 269; 

of food in roots, 81 ; 

of insects, 225, 243, 244, 245, 246, 
247, 248, 249; 

of leaves, 112; 

of lobster, 212; 

of moUusks, 255, 256, 258j 

of parasitic worms, 203^ 

of plants, 146; 

of snakes, 283; 

of starfish, 258; 



INDEX 



445 



Economic importance, of toads, 
279; 

of trees, 115, 117. 
Ectoderm, defined, 182. 
Egg, development of, 182. 
Egg cell, 26, 182, 266, 276. 
Egg-laying habits of fishes, 266. 
Elasmobranch, 271. 
Embryo sac, 26, 132. 
Endoderm, defined, 182. 
Endoskeleton, 261, 265. 
Endosperm, use of, 57, 68, 64, 65; 
Energy, defined, 9. 
Entomostraca, 232. 
Environment, 6. 

Enzyme, action upon fibrinogen, 
359; 

in saliva, 347. 
Enzymes, 58, 344; 

in gastric juice, 349. 
Epicotyl, 54, 55. 
Epidermis, 313. 
Epiglottis, 345. 
Erosion, by streams, 115, 116; 

prevented by organic covering, 
117. 
Esophagus, 343, 345, 348. 
Eustachian tube, 345, 397. 
Excretion, in crayfish, 209; 

organs of, 188; 

organs of, in man, 383, 384. 
Excurrent tree, 84. 
Exercise, and health, 407; 

in hygiene, 412. 
Exoskeleton, 205. 
Expiration, 376. 
Eye, care of, 400; 

coats of, 398; 

defects in, 399; 

human, 398; 

image formed inj 400: 

of crayfish, 206; 

of insect, 219. 

Facets, 219. 
Fallowing, 80. 
Family, defined, 134. 
Fatigue, 371. 
Fats, 14, 323; 
test for, 14. 



Fermentation, chemistry of, 149. 
Fern, life history of, 132. 
Fertilization, 26, 27, 131. 
Fevers, cause of, 387. 
Fibrin, 359. 
Fibrinogen, 359. 
Fibrovascular bundles, 74; 

of a monocotyledon, 92 ; 

use of, 85. 
Filament, 25. 

Fish hatchery, work of, 270» 
Fishes, appendages of, 2613 

body of, 261; 

classification of, 271; 

migration of, 268; 

protection of, 269. 
Fission, 174. 
Flagella, 183. 
Flatworm, 199. 
Fhcker, 298. 
Flower, defined, 24; 

dimorphic, 34; 

fertilization of, 25; 

pistillate, 38; 

relation to fruit, 54; 

staminate, 38; 

structure of, 24; 

trimorphic, 35. 
Flowers, work of, 24. 
Fly, foot of, 224; 

head of, 31; 

typhoid, 224, 225, 
Food, 13; 

and dietaries, 322; 

and disease, 420; 

and health, 406; 

economy, 331; 

in hygiene, 411; 

laws, 335; 

necessity of, 395; 

storage in stem, 92; 

swallowing of, 348; 

vacuoles, 173; 

waste in kitchen, 333, 334; 

why we need, 322, 
Food taking, in birds, 294; 

m clams, 253; 

in crayfish, 207; 

in earthworm, 196, 197; 

in fishes, 265; 



446 



INDEX 



Food taking, in frogs, 274; 

in grasshopper, 219; 

in hydra, 184; 

in snakes, 283; 

in starfish, 259; 

in turtles, 281; 

organs of, 188. 
Foods, absorbed into the blood, 352, 
354; 

adulterations in, 335; 

costs of various, 330; 

inorganic, 15, 324; 

organic, 13; 

values of, 328. 
Forest destruction, 121, 122. • 
Forest regions in United States, 118. 
Forester, and his work, 124. 
Forestry, 122. 
Forests, protection of, 123; 

their uses and protection, 115. 
Frog, leopard, 272, 273 ; 

study of, 272- 

tree, 279. 
Fronds, 132. 
Fruit, defined, 41; 

stages in formation of, 40. 
Fruits, and their uses, 40; 

dehiscent, 44; 

economic value of, 47; 

garden, 52; 

indehiscent, 45; 

orchard, 52. 
Functions, of parts of an animal, 18, 
188; 

of parts of a plant, 17. 
Funiculus, 41. 
Fungi, 130; 

parasitic, 152, 153; 

saprophytic, 148, 149, 151, 

GaU bladder, 343, 351. 
Gametoph^-te, in moss, 131, 132. 
GangUa, 390. 
Ganoid, 271. 
Gastric juice, 349. 
Gastric miU, 209. 
Gastropods, 256, 259. 
Gastmla, 182. , 

Genus, defined, 133. 
Geotropism, 71. 



Germination^ factors in, 60; of 

bean, 63. 
Gila monster, 282. 
Gill rakers, 263; 

in shad and bluefish, compared, 
266. 
Gills, fish's, structure of, 263. 
Girdle, pectoral, in man, 319; 

pehdc, in man, 319. 
Glands, defined, 344; 

ductless, secretions of, 368; 

gastric, 348, 349; 

intestinal, 352; 

l5Tnph, 369, 370; 

salivar\', 347; 

structure of, 344; 

sweat, 384. 
Glomerulus, 384. 
Glycogen, formation of, 352= 
Goldfinch, American, 296, 
Grafting, 94. 
Grain, 45, 46. 
Grape sugar, test for, 14. 
Grasses, production of, 50. 
Grasshopper, red-legged, 217= 
Guard cell-, 103. 
GuUet, 343, 345, 348. 
Gymnosperms, 134. 

Habit, alcohohc, 401. 

Habits, formation of, 394. 

Hsemoglobin, 360. 

Haemolysins, 358. 

Hair, development of, 313. 

Halophytes, 138. 

Hammer, 397. 

Ha}' infusion, life in, 170. 

Health, and disease, 404; 

department of, 419; 

department of, work of, 419; 

good, and how to keep it, 404. 
Hearing, organ of, 397. 
Heart, a force pump, 364; 

in action, 364; 

ners'ous control of, 370; 

position of, 363; 

protection of, 363; 

structure of, 363; 

valves in, 363. 
Heliotropism, 99, 100. 



INDEX 



447 



Hemiptera, 227, 232. 

Heredity, 67. 

Hilum, 54. 

Honeybee, 238. 

Hookworm, 200. 

Hormones, work of, 350. 

Hornets' nest, 239. 

Horse, geologic history of, 307. 

Hmnan body a machine, 312. 

Humus, 10, 78. 

Hybridizing, 68. 

Hybrids, 39, 68. 

Hydra, 184. 

Hydrophytes, 137. 

Hygiene, Fisher's rules of, 410; 

personal, 404; 

pubUc, 415. 
Hymenoptera, 229, 232. 
Hypha, 150. 
Hypocotyl, 54, 55. 

Ichneumon fly, 242. 

Immunity, 421. 

Inorganic soil, relation to organic, 78. 

Insects, 216; 

and crustaceans compared, 231; 

beneficial, 249, 250; 

characteristics of, 229; 

communal life, 237; 

control of damage by, 249, 250, 
251; 

disease-carrying, 243, 244, 245; 

divisions of, 232; 

muscular activity of, 219; 

noxious, 245, 246, 247, 248, 250, 
251; 

relation to mankind, 242; 

«ense of smell, 31; 

sight of, 31; 

winners in life's race, 216. 
Inspiration, 376. 
Intestine, large, 343, 354; 

small, 343, 352; 

small, stracture of, 353. 
Invertebrate, cross section of, 260. 

Joint, hinge, 316. 

Key fruit, 46. 



Kidney, human, 383, 384. 
Knots, cause of, 120, 121. 

Lacteals, 354, 370. 

Larva, 222, 223. 

Larval stages, defined, 182. 

Lateral Hne, function of, 263. 

Leaf, cell structure of, 103, 104; 

respiration in. 111; 

structure of, 102, 103. 
Leaves and their work, 98; 

arrangement of, 101; 

as insect traps, 113; 

modified, 112, 113. 
Legs, of grasshopper, 217. 
Lens of eye, 399. 
Lenticels, use of, 85. 
Lepidoptera, 232. 
Levers, classes of, 317; 

in body, 316. 
Lichens, 168. 
Life history, of aphid, 228; 

of beetle, 227; 

of butterfly, 221, 222; 

of cecropia, 223; 

of Chinook salmon, 267; 

of cicada, 227, 228; 

of fly, 224, 225; 

of frog, 276, 277, 278; 

of grasshopper, 220; 

of honeybee, 239; 

of lobster, 211; 

of mosquito, 243; 

of yellow perch, 267. 
Light, effect of, upon plants, 98, 99, 

100. 
Lily, leaves of, 101. 
Liver, 343, 351. 

Living matter, composition of, 12. 
Living things, environment of, 6; 

functions and composition of, 17. 
Lizards, 282. 

Lobster, North American, 209, 210. 
Locomotion, in crayfish, 205; 

in frogs, 273: 

in snakes, 283; 

of earthworm, 196; 

organs of, 188. 
Locust, relatives of, 220. 
Lumber, transportation of, 119, 121. 



448 



INDEX 



Lymph, defined, 369; 

function of, 369. 
Lymph vessels, 369, 370. 

Macronucleus, 173, 174. 
Malacostraca, 232. 
Malaria and the mosquito, 178, 243. 
Mammal, circulation in, 365; 

man a, 311. 
Mammals, 303; 

classification of, 309; 

hoofed, 306. 
Man, brain of, 391; 

circulation in, 362; 

evolution of, 311; 

mouth cavity of, 346; 

place of, in nature, 311; 

races of, 312; 

stomach of, 343, 349. 
Mandible, 218, 219. 
Mantle cavity, 253. 
Marsupials, 309. 
Maxilla, 218, 219. 
MaxilUpeds, 207. 
May flies, 229. 
Medulla, 391. 
Medusa, 190. 

Membrane, tympanic, 397. 
Mendel, Gregor, 68. 
Mesoderm, 182. 
Mesophytes, 138. 
Metazoa, 181. 
Micronucleus, 173, 174. 
Micropyle, 26; of bean, 54; 
Mildews, 153. 
Milk, an emulsion, 351; 

and typhoid, 418; 

bacteria in, 159; 

necessity of pure, 416, 418. 
Milkweed, dispersal in, 66. 
Mimicry in insects, 236, 237. 
Mineral matter, in living things, 12. 
Molars, 346. 
Mold, 149, 150. 
Mollusks, 253; 

classification of, 259; 

habitat of, 257; 

some common, 254, 255, 256, 257. 
Molting, 211. 
Monarch butterfly, 236. 



Monocotyledons, 59. 

Monotremes, 309. 

Mosquito, and malaria, 178, 243; 

and yellow fever, 244; 

kinds of, 243; 

malarial, 178, 243. 
Mosses, 130, 131. 
Moth, compared with butterfly, 

222, 223. 
Mouth, 343; 

of grasshopper, 218. 
Mouth cavity, of man, 345. 
Mucus, 344. 

Muscle tissue, use of, 315. 
Muscles, and skeleton, 316; 

arrangement of voluntary, 314; 

extensor, 314; 

flexor, 314; 

nerve endings in, 315; 

of frog's leg, 314; 

structure of voluntary, 315. 
Mushrooms, 151. 
Mutant, 68. 
Mutation, 68. 
^Mycelium, 150. 
Myriapods, 230, 232. 

Nails, development of, 313. 

Narcotic, defined, 339. 

Natural resources, conservation of, 4. 

Nectar, defined, 31. 

Nectar glands, 31. 

Nectar guides, 31. 

Nerve, optic, 398; 

parts of, 390. 
Nerve cells, 391. 
Nerve fibers, 391. 
Nerves, mixed, 392; 

motor, 392; 

sensory, 392; 

vasomotor, 370. 
Nervous control, of blood vessels, 
370; 

of heart, 370; 

of respiration, 377; 

of sweat glands, 386; 

organs of, 188. 
Nervous system, and sense organs, 
390; 

autonomic, 392; 



INDEX 



449 



Vervous system, cerebrospinal, 390; 

divisions of, 390; 

functions of, 321; 

in birds, 291; 

in fishes, 265; 

in man, 321; 

of crayfish, 209; 

of frog, 392; 

of insects, 220. 
Neuroptera, 228, 232. 
Newt, 279. 
Nicotine, 339. 
Nictitating membrane, 273. 
Nitrogen, in plant growth, 79, 80; 

properties of, 7. 
Nitrogen cycle, 167, 168. 
Nitrogen-fixing bacteria, 157, 158. 
Nucleolus, 20. 
Nucleus, 20; 

in amoeba, 175. 
Nutrients, 13, 322; 

fuel values of, 326; 

in beans, 56; 

uses of, 326. 
Nymph, 229. 

Oak, section of, 86. 
Oats, production of, 49. 
Oils, 14, 323; 

test for, 14, 
Ommatidia, 207. 
One-celled animals, 177. 
Operculum in fishes, 263. 
Opossum, Virginia, 309. 
Opsonin, 361. 
Orbit, 398. 
Orchid, wild, 28, 
Organ, defined, 17, 134, 186. 
Organic and inorganic 'matter, 21. 
Organism, defined, 17. 
Organs of a plant, 18. 
Oriole, Baltimore, 299. 
Qrthoptera, 232. 
Osculum, 183. 
Osmosis, 75; 

importance of, 76; 

of sugar, 89, 347. 
Ovary, 25. 
Ovipositor, 218. 
Ovule, deyelopment of, into seed, 27- 



Owl, screech, 299. 
Oxidation, defined, 8; 

heat the result of, 9; 

in germination, 62; 

in human body, 11; 

of carbon, 11; 

rapid, 11; 

slow, 9. 
Oxygen, evolved in starch making, 
109; 

in air, 7; 

preparation of, 8; 

properties of, 8. 
Oyster, 255. 

Palate, hard, 345; 

soft, 345. 
Pancreas, position of, 343, 350. 
Pancreatic juice, function of, 351. 
Papillge, 345. 
Pappus, 43. 
Paramecium, 172, 173; 

reproduction of, 174; 

response to stimuli in, 173. 
Parasites, 130. 
Parasitism, in insects, 242. 
Pasteurizing, 158. 
Patent medicines, alcohol in, 340. 
Pearl formation, 256. 
Peas, as food, 56. 
"Peepers," 279. 
People, 52. 
Pepsm, 349. 
Pericardium, 363. 
Perspiration, insensible, 385. 
Petal, 24. 
Phagocytes, 361. 
Pharynx, 345. 
Phloem defined, 88. 
Phcebe, 297. 
Photosynthesis, 106. 
Physiology, defined, 1; 

human, 1. 
Pigeon-wheat moss, 130, 131 
Pistil, 251. 
Placenta, 41. 

Plant and animal compared, 17 
Plant body, simplest, 126. 
Plant breeding, 66. 
Plant invasions, 144. 



450 



INDEX 



Plant life, in temperate zones, 142; 

forms of, 126; 

in tropics, 140; 

upon mountains, 141. 
Plant modification, cold a factor in, 
140; 

water a factor in, 137, 138; 

wind a factor in, 139. 
Plant outpost, a, 145. 
Plant societies, 142, 143. 
Plants, adaptation to environment, 
144; 

beneficial and harmful, 146; 

classification of, 134; 

harm done by, 146; 

modified by surroundings, 136, 
137; 

relations to animals, 2, 4, 166, 
167. 
Plasma of blood, 358. 
Pleura, 375. 
Pleurococcus, 128, 172. 
Plumule, 54, 55. 
Pocket garden, 71. 
Pollen carriers, 32, 33. 
PoUen, growth of, 25; 

protection of, 38. 
Pollination, 27; 

artificial, 38; 

by humming bird, 32 ; 

by insects, 29; 

by wind, 36, 37; 

history of, 27. 
Polycotyledons, 59, 60. 
Polyps, coral, 192; 

hydroid, 190. 
Pome, 52. 
Pond lilies, 136. 
Pond scum, 129. 
Pons, 391. 

Potato beetle, 227, 246. 
Potato tuber, 95. 
Precipitins, 358. 
Premolars, 346. 
Proboscis, 32. 

Proglottids of tapeworm, 199. 
Pronuba, 35. 

Protective resemblance, 234, 235. 
Protein, in bean, 56. 
Protein making in plant, 107. 



Proteins, 15, 323; 

building of, 90; 

test for, 15. 
Prothallus, 132. 
Protonema, 131. 
Protoplasm, composition of, 22; 

properties of, 22. 
Protozoa, 172; 

classification of, 180; 

habitat of, 177; 

relation to disease, 178; 

use as food, 178. 
Pseudopodia, 175. 
Pteridophytes, 134. 
Ptomaines, 157. 
Ptyalin, 348. 
Pulmonates, 257. 
Pulse, cause of, 366. 
Pupa, 222, 223. 
Pupil, 398, 399. 
Pylorus, 348. 

Quarantine, 421. 
Queen, 238. 

Radiolarian, 180. 

Ray flower, 34. 

Rectum, 343. 

Reflex action, examples of, 393; 

meaning of, 393; 

nervous, 393. 
Regeneration, defined, 198. 
Relation, of birds and reptiles, 301; 

of body heat to work, 385; 

of breathing to exercise, 381; 

of environment to diet, 329; 

of flies to disease, 225; 

of Protozoa to disease, 178; 

of work to diet, 329. 
Rennin, 349. 
Reptiles, study of, 281; 

classification of, 285. 
Reproduction, in animals, 182; 

in plants, 181; 

organs of, 188. 
Respiration, 374; 

adaptation for, 375; 

artificial, 381, 382; 

effect of alcohol on, 388; 

effect of tobacco on, 388; 



INDEX 



451 



Respiration, excretion^ 374; 

in a cell, 383; 

in birds, 291; 

in crayfish, 207; 

in fishes, 263; 

in frog, 274; 

in insects, 218; 

necessity for, 374; 

nervous control of, 377; 

organs of, in man, 374. 
Rest, necessity of, 395, 412. 
Retina, 398, 399. 
Rhizoids, 130, 150. 
Ribs, attachment of, 318; 

in respiration, 376. 
Rice, production of, 50. 
Robin, 295. 
Rodents, 305. 
Root, absorption in, 75; 

effect of moisture on, 71, 72; 

food storage in, 81; 

influence of gravity upon, 70; 

passage of soil water in, 76; 

tip of, 73. 
Root hair, structure of, 74. 
Root hairs, 74. 
Root pressure, 91. 
Root system, 70. 
Roots, and their work, 70; 

different from stems, 98; 

modified, 81, 82. 
Roundworm, 199. 
Rye, production of, 50. 

Salamander, spotted, 280. 
Saliva, function of, 347. 
Salmon leaping a fall, 268. 
San Jose scale, 248. 
Sand shark, 271. 
Sanitation, public, 415. 
Saprophytes, 130. 
Sea anemone, 191. 
Sea lion, 304. 
Seaweeds, 126. 
Seed dispersal, 41, 42, 66. 
Seedling, defined, 64. 
Seeds, and seedlings, 54; 

formation of, 41; 

uses of, 65; 

winged, 44. 



Selective absorption, 176. 
Selective breeding, 308. 
Selective planting, 67. 
Self-pollination, defined, 27. 
Sense organs, 188, 219, 273; 

in birds, 291; 

in fishes, 262; 

in man, 395. 
Sepal, 24. 

Serum of blood, 359. 
Sexual development of simple ani- 
mal, 182. 
Sexual reproduction, in animals, 
174, 177, 184, 190, 191, 266, 276; 

in plants, 130, 131, 132. 
Shelf fungus, 151. 
Ship worm, damage by, 258. 
Shrimps, 212. 
Silkworm, 4, 223. 
Skeleton, and muscles, 316; 

appendicular, 318; 

axial, 318; 

of birds, 289; 

of dog, 318; 

of fishes, 265; 

of man, 319; 

structure of, 317; 

uses of, 317. 
Skeleton building in Protozoa, 180. 
Skin, hygiene of, 386; 

structure of, 313. 
Skull, of boa constrictor, 284; 

of dog, 304; 

of man, 320; 

of porcupine, 305. 
Sleep, and health, 407; 

necessity of, 395. 
Smell, organs of, 396. 
Snail, 256. 
Snake, garter, 283. 
Snakes, poisonous, 284; 

value of, 283. 
Soil, composition of, 10, 77; 

organic matter in, 78; 

water in, 77, 79; 

weathering of, 77. 
Soil exhaustion, prevention of, 80. 
Sparrow, English, 299; 

song, 295. 
SpecieS; defined, 133. 



452 



INDEX 



Spermatophytes, defined, 133, 134. 

Sperm cell, 25, 182. 

Spiders, 230. 

Spinnerets of spiders, 230. 

Spiracles, 218. 

Spirillum, 154, 

Spirogyra, 129. 

Sponge, structure of, 183. 

Sponges, 189. 

Sporangium, 150. 

Spores, 150. 

Sporophyte, in moss, 131. 

Squash bug, 246. 

Squid, 257. 

Stamens, 25. 

Starch, in bean, 55; 

non-osmosis of, 89, 347; 

test for, 13, 14; 

to grape sugar, 57. 
Starch grains, 55. 

Starch making, and milling, com- 
pared, 106; 

by green plants, 104; 

chemistry of, 106, 107; 

light and air in, 105; 

rapidity of, 108. 
Starfish, 258. 
Stem, dicotyledonous, 85, 86,; 

dicotyledonous and monocoty- 
ledonous, compared, 92; 

modified, 94, 95; 

monocotyledonous, 91; 

movement of fluid in, 88, 90; 

structure and work of, 84. 
Stems, 95, 96. 
Sternum, 319. 
Stigma, 25. 
Stimulants, 336. 
Stimuli, response to, in Paramecium, 

173. 
Stirrup, 397. 
Stomach, movements of, 350; 

of man, 343, 348, 349. 
Stomata, 104, 111. 
Street cleaning, 415, 416. 
Struggle for existence, 46. 
Sturgeon, 271. 
Style, 25. 
Suffocation, 381. 
Sugar, osmosis of, 89, 347. 



Sun, a source of energy, 102. • 
Sunlight, in starch making, 105. 
Swallow, barn, 297. 
Swarming, 240. 
Sweat, 385. 
Sweat glands, 313; 

nervous control of, 386; 

structure of, 384; 

use of, 384. 
Sweeping, 380. 
Swim bladder, 264. 
Swimmerets, 206. , 
Symbiosis, 168; 

between plants and insects, 241; 

in crabs, 214; 

inhchens, 168, 169; 
Synura, 128. 
Systematic botany, 133. 

Tail of birds, function of, 289. 

Tapeworms, 199. 

Taproot, 72; 73. 

Tarantula, 230. 

Taste, organs of, 396. 

Taste buds, 345, 396. 

Teeth, canine, 304, 346; 

care of, 346; 

incisors, 346; 

kinds of, in man, 346. 
Teleosts, 271. 
Temperature, feeling of, 396; 

in germination, 61. 
Tentacles, 184. 
Testa, 54. 
Tetanus, 162. 
Thallophytes, 134. 
Thallus, 126. 
Theine, 336. 
Thoracic duct, 370. 
Thoracic region, 319. 
Thorax, 217. 
Throat, 343. 
Timber, cutting of, 120. 
Tissue, 19, 186, 314. 
I'issues, of human body, 186. 
Toad, common, 278. 
Tobacco, effect on nervous system, 
339; 

effect on respiration, 388; 

use of, 339. 



INDEX 



453 



Tongue, 343, 345. 
Tonsil, 345. 
Tooth, section of, 346. 
Tortoise, box, 282. 
Touch, experiment in, 396; 

organs of, 395. 
Toxin, 159. 
Tracheae, 218, 345. 
Transpiration, in plants, 110, 111. 
Tree, wounded by "cribbing," 123, 

124. 
Trees, city's need for, 124. 
TrilUums, 144. 
Trypanosomes, 179. 
Tuberculosis. 160; 

death rate from, 424 ; 

fighting, 419, 420. 
Turtle, 281. 

Tussock moth, larva of, 247. 
Typhoid fever, 161; 

due to milk supply, 418; 

due to water supply, 417 ; 

fighting, 419. 

Undent' ing moth, 235. 
Ungulates, 306. 
Urea, 384. 
Ureter, 384. 
Urethra, 384. 
Uropod, 207. 

Vaccination, 422. 

Vacuole, contractile, 173, 174, 175, 
176; 

food, 173, 175, 176. 
Valves, 41. 
Veins, 362; 

function of, 367; 

structure of, 367. 
Ventilation, methods of, 379; 

need of, 379; 

of sleeping rooms, 381. 
Ventricle, 363. 
Venus's flower basket, 189. 
Venus's flytrap, 113. 
Vermiform appendix, 343, 355. 
Vertebra, 318. 



Vertebral column, 318, 319. 
Vertebrates, compared with inver- 
tebrates, 260. 
Vicerov butterfly, 236. 
Vilh, 353. 

Vitamins, 323, 324, 325. 
Vitreous humor, 398, 399. 
VorticeUa, 177. 

Walking sticks, 234. 
Warbler, yellow, 297. 
Warning coloration, 236. 
Wasp, solitary, 237. 
Water, and health, 406; 

and typhoid, 417; 

composition of 9, 10; 

factor in germination, 60, 61; 

in hygiene, 411; 

in hving things, 12; 

necessity of pure, 416, 417. 
Water supplj^, factor in modification, 
137; 

regulated by forests, 115, 116. 
Weathering, 77. 

Web, spider's, uses and forms, 230. 
Weed, 17, 46. 
Wheat, production of, 49; 

uses of, 49. 
Wheat rust, 152. 
Wings, of grasshopper, 218. 
Wood, structure of, 120; 

uses of, 119. 
Woodpecker, downy, 298. 
Worker, 238. 
Worms, classification of, 202; 

harmful, 198: 

study of adaptation-s, 194. 
Wren, house, 296. 

Xerophytes, 137. 
Xylem, defined, 88. 

Yeast, 148, 149. 
YeUow fever, 244. 

Zvgospore, formation of, 129, 130, 
150. 



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